Small ruminants grazing native vegetation select their diet from a wide variety of plant species, which differ in content and nutrient availability during the year, and are important sources of nutrients. The objective of this study was to determine and compare the biochemical composition of rangeland forage species in Baja California Sur. The species evaluated were huizache, mezquite, palo fierro, palo verde and vinorama, as well as alfalfa hay. The dry matter, crude protein, total lipids, crude fiber, ash, nitrogen free extract and gross energy content were quantified as well as the concentration of linoleic acid, α-linolenic acid and polyunsaturated fatty arachidonic (ARA), eicosapentaenoic (EPA) and docosahexaenoic acids (DHA). The results showed that palo verde and mesquite had a higher content of protein crude. Huizache showed the highest concentration of total lipids followed by palo verde and mezquite. Huizache and alfalfa hay showed higher concentrations of linoleic acid, while palo verde reached higher levels of α-linolenic acid, followed by palo fierro and alfalfa hay. Forages species with higher concentrations of polyunsaturated fatty acids included palo verde, palo fierro and alfalfa hay. The use of rangeland forage in the diet of ruminants is an alternative that may change the proportions of milk fatty acid content due to the oleic acid and linoleic and linolenic acid content, vaccenic and rumenic acids precursors and polyunsaturated fatty acids series such as omega 3 EPA and DHA. [ABSTRACT FROM AUTHOR]