The kernels of Irvingia specie have been reported to used as soup thickener in some parts of Nigeria and also rich in protein, glucose, fat and oil and fatty acids. Hence, this research aims to assess the effect of Irvingia fruit kernel on the mean population density of Bacillus spp. Eleven isolates were identified as suspected Bacillus species using standard microbiological and biochemical testing techniques. Irvingia broth, Irvingia broth/tryptone (50/50) and tryptone soya broth were prepared, and Bacillus isolates were inoculated into the different broths and incubated at 300C for 14 days. All isolates were Gram positive, indole and oxidase negative, citrate negative (except isolate M1) and catalase negative (except Isolates F2,F3,FW2, FW3 and FW4). The maximum mean population density of Bacillus spp in Irvingia and Irvingia/Tryptone broths in Day1,3,7,10 and 14 were 3.1 x 108 cfu/ml (Irvingia/Tryptone), 3.1 x 108 cfu/ml (Irvingia), 3.1 x 108 cfu/ml (Irvingia and Irvingia/Tryptone), 4.0x108 cfu/ml (Irvingia and Irvingia/Tryptone) and 4.0x108 cfu/ml (Irvingia) respectively. The findings in this research signifies that Irvingia and Irvingia/Tryptone broths can support the growth of Bacillus spp just like tryptone soya broth.