SUMMARY Probiotic microbial feed supplements are gaining wide acceptance in livestock production, and may be applicable to aquaculture production systems. The present study was designed to investigate the effect of incorporation of probiotics (Bacillus subtilis and Biogen®), spices (garlic or fennel) and also a combination of B. subtilis with garlic or fennel in the diets of Nile tilapia Oreochromis niloticus. A total of 420 Nile tilapia fry were divided into seven treatments (3 replicates for each treatment) and fed the experimental diets for 90 days. The basal diet was fomulated to contain 30% CP and 2700 Kcal ME kg-1 and divided into 7 diets. The 1st one as a control diet (D1). The other diets were supplied by the diffeent additives, B. subtilis (D2), 0.2% Biogen® (D3), 1% garlic (D4), 1% fennel (D5), B. subtilis+1% garlic (D6) and B. subtilis+ 1%fennel (D7). Results of the present experiment indicated that, supplementation of the basal diets with probiotics B. subtilis or Biogen® and spices (garlic or fennel) significantly (P