Effects of supplementing diet with methanol extract of Pseuderatherum palatiferum leaf on growth performance, haematology, immune response and resistance againts Streptococcus agalactiae was investigated in Nile tilapia (Oreochromis niloticus). The extract was mixed in commercial feed with 3 different doses (0.01,0.1and 0.5 percent w:w,respectively) and fed to Nile tilapia (initial weight of 35.80+0.41g.) for 8 weeks. The best growth performance in term of final weight gain and specific growth rate (SGR) was observed in the treatment of diet containing 0.5 percent extract. The results of haematological study in 8th week showed that all parameters from each treatment were not statistically different. Fish fed with 0.1 and 0.5 percent extract had significantly increased in respiratory burst activity and serum bactericidal activity. The lowest mortality was observed in fish fed with 0.5 percent extract after 10 day challenged with S.agalactiae. It was cocluded that extract of P.palatiferum at 0.1 and 0.5 percent can be used to improve the growth performance, immune activity and resistance to S. agalactiae in Nile tilapia.