Excretory/secretory antigen was prepared by culturing live adult worms of Haemonchus contortus in RPMI 1640 medium at a concentration of 50 worms per mL in a culture-flask at 37oC for 24 hr and the culture supernatant was used as antigen. The E/S antigen was purified by thiol-sepharose affinity chromatography. On western blot analysis, it was demonstrated that thiol-purified antigen showed a single reactive band at 66 kDa. In immunization trial, sheep were administered intramuscularly with 500 mg of thiol-purified excretory/secretory antigen along with montanide as adjuvant on day 0, 30 and 60. On ELISA, it was observed that the mean absorbance values were significantly (p£0.01) higher up to 20 weeks post immunization in Group-I (purified antigen) compared to Group- II (unimmunized control). Further, the mean EPG values was lower in Group I (200.00±40.82 to 400.00±91.29) than Group II (2200.00±108.01 to 5100.00±169.56) and the percentage reduction in mean fecal egg counts was 88.50%. Similarly, the mean abomasal worm counts was lower in Group I (808.33±78.29) than Group II (3280.00±147.19) and the percentage reduction in mean abomasal worm count was 75.40%.