Phytogenic feed additives, also called as phytobiotics or botanicals, are plant-derived compounds added into diets to enhance the productivity of poultry. This study was conducted to investigate the effect of administration of Satureja khuzestanicaessential oils (SKEO) through drinking water on immune performance of broiler chicken using 720 one-day-old Arian chicks. The birds were raised under standard production practices up to 42 days of age. The birds continuously received drinking water treated with Tween 80 (Cont+; 500 ppm) or SKEO at 0 (Cont-), 200, 300, 400 and 500 ppm. The mean hemagglutinin inhibition (HI) antibody titer was not significantly different among the treatments at 15, 21, 28 and 35 days of age (P>0.05). No significant differences were pointed out for relative weight of spleen, bursa and thymus at 21 days. Thymus weight reduced for the birds that received treated water but a difference was only significant for 400 ppm SKEO. The mean hetrophyle lymphocyte ratio was not significantly differing among the treatments. It is concluded that supplementation of broiler chicken drinking water with S.khuzestanica essential oils has no favorite impact on immune response of heat stressed broiler chicken. Key words: Satureja khuzestanica, immune system, broiler chicken.