Introduction1 Medicinal plants have a long history of treating different diseases. Glaucium flavum (yellow horned poppy) is a summer-flowering plant in the family Papaveracae. It is native to Northern Africa, Macaronesia, temperate zones in Western Asia, and the Caucasus, as well as Europe. It has thick, leathery deeply segmented, wavy, bluishgrey leaves, which are coated in a layer of water-retaining wax. Yellow Horne Puppy (YHP) is an alkaloid medicinal plant with a high content of antioxidants and anti-inflammatory properties. This study aimed to evaluate the effect of hydro-alcoholic extract of Yellow Horne Puppy on some hematological indices in male rats compared with vitamin C. Vitamin C is an electron donor, and this property accounts for all its known functions. As an electron donor, vitamin C is a potent water-soluble antioxidant in humans. Materials and Methods In this experimental study, 36 adult male Wistar rats were randomly divided into six groups (six rats in each group): (1) The first group (control) did not receive any dose, and the experimental groups (2) treated with oral administration of 250 mg/kg of yellow horned poppy extract, (3) treated with Intra-peritoneal (IP) administration of 250 mg/kg of the extract and 100 mg/kg of vitamin C, (4) treated with IP administration of 100 mg/kg of vit C, (5) treated with oral administration of 500 mg/kg of extract, (6) treated with oral administration of 200 mg/kg of vit C. Thirty days after administration following induction of anesthesia and taking blood from the heart of rats, blood samples were collected and hematological parameters measurement including red and white blood cells, hemoglobin, hematocrit, mean corpuscular volume, mean corpuscular hemoglobin, mean corpuscular hemoglobin concentration, Red blood cell distribution width and platelets measured by a Hematology Auto Analyzer. The obtained data were subjected to the Shapiro-Wilk test for normality. Results were analyzed statistically by SPSS software version 22 and the One-way ANOVA test with Bonferroni post hoc test. Mean ± SD was considered significant if (P<0.05). Results and Discussion Medicinal plants have natural ingredients and many of these plants have fewer side effects. Because the most important known factor in yellow horned poppy is its alkaloids. The most important alkaloids of this plant include Glaucine, Berberine, Bolbucapanine, and Protopine. Glaucine is an alkaloid that has been shown to have antioxidant properties and can protect against double bond fatty acids against free radicalmediated peroxidation. Due to our result, the oral consumption of yellow horned poppy significantly increased the number of Neutrophils (76.84±14.02) and, decreased Lymphocytes (18.41±9.58). Elevated blood neutrophils due to the induction of stressful conditions and stimulation of the immune system. In this sense, these factors not only raise white blood cells but also affect other blood parameters but, in this study, Changes in white blood cell counts due to oral administration and injecting vitamin C have been shown to stimulate the immune system. Injection of vitamin C showed a significant increase in monocytes (4.16±0.75). The number of red blood cells among the groups under study showed no decreasing or increasing effect (P>0.05). Hb and MCH increased with both oral and IP administrated extracts. IP administration of YPH+vit C has led to a decrease in MCH and MCHC (17.56±0.66, 33.76±0.80). Platelets were also significantly increased by IP administration of Extract of Glaucium Flavum+ vitamin C (351000±126714). The rate of RDW was reduced by oral administration of YPH and injection (13.01±1.35, 12.73±0.53). Glaucium flavum contains Glaucine, an alkaloid similar in effect to codeine, in that it has cough suppressant activity but without being addictive. Glaucine is an alkaloid found in several different plant species such as Glaucium flavum, Glaucium oxylobum, Croton lechleri, and Corydalis yanhusuo. It has a bronchodilator and anti-inflammatory effects, acting as a PDE4 inhibitor and calcium channel blocker, and is used medically as an antitussive in some countries. Glaucine may produce side effects such as sedation, fatigue, and a hallucinogenic effect characterized by colorful visual images and has recently been detected as a novel recreational drug. Conclusion The findings of this study reveal that Oral administration of the yellow horned poppy extracts can have a good effect on blood parameters, as same as vit C, due to its antioxidant properties. Therefore, this plant extract can be used in the treatment of many diseases. [ABSTRACT FROM AUTHOR]