Abstract: The effect of oral administration of different doses of probiotic, Lactobacillus plantarum, isolated from fermenting corn slurry on the haematological parameters of wistar albino rats was investigated. Sixteen (16) rats divided into four groups (A, B, C and D) of four rats per group were used. Group A was placed on the basal diet alone, while group B, C and D were placed on the diet and also dosed with 0.3ml, 0.6ml, and 1.0ml of 107 cfu/ml of reconstituted lyophilized culture of Lactobacillus plantarum respectively. In rats treated with different doses of Lactobacillus plantarum there was a significant increase in the packed cell volume (PCV), haemoglobin and red blood cell (RBC) when compared with the control. Moreover, the differential leucocyte counts reveal an increase in the lymphocyte count of the rats dosed with Lactobacillus plantarum when compared to the control except in rats dosed with 1.0ml of 107 cfu/ml of the probiotic, which was not significantly different (P<0.05) from the control. There was also a significant increase (P<0.05) in the weight gain by rats fed Lactobacillus plantarum when compared to the control. The data obtained showed that Lactobacillus plantarum isolated from fermenting corn slurry is safe and it has immunostimulatory effect and can also improve the performance of rats in terms of weight gain.