A 42 day feeding trial involving twenty five, seven weeks old male grass cutters with an initial weight of 604.9 -609.7g was conducted to determine the growth response and carcass characteristics of weaner grass cutters fed diets supplemented with P. longifolia seed oil as a natural growth promoter. Five diets were formulated to contain basal diet + 0% P.longifolia oil and Oxytetracycline for T1 this served as negative control while T2 was fed basal diet containing Oxyteteracycline (synthetic growth promoter) as positive control at 25mg/kg, T3, T4 and T5 were fed basal diet supplemented with P. longifolia oil as natural growth promoter at 0.2%, 0.3% and 0.4% respectively. The grass cutters were randomly divided into five groups of five grass cutters each with each grass cutters serving as replicate in a completely randomized design experiment. Feed and clean water were provided ad libitum. There was a significant (P<0.05) differences among the treatments for final live weight, feed conversion ratio, carcass weight and dressing percentage. There was no significant differences (P>0.05) in mortality, feed intake, daily water intake, feed cost per kg and relative weights of the organs examined ( liver, kidney, heart, spleen, testis, intestine and abdominal fat). The result of this study indicates that the inclusion of P. longifolia oil up to 0.40% has no deleterious effect on the performance and health status of grass cutters.