Batch propionic acid fermentation kinetics was studied using five different initial concentrations of lactose (i.e., 37 g/L, 45 g/L, 50 g/L, 57 g/L and 73 g/L) at constant temperature (30 degrees C) and pH (6.5) under anaerobic conditions using Propionibacterium acidipropionici (ATCC 4875). When the initial substrate concentration was 37 g/L, 45 g/L, 50 g/L, 57 g/L and 73 g/L, then, correspondingly, 16 g/L, 19 g/L, 22.25 g/L, 25.3 g/L and 26.3 g/L of propionic acid was accumulated in the fermentation broth. Increasing the supply of lactose in the fermentation medium led to the accumulation of by products succinate, acetate and pyruvate. Maximum propionate yield (0.44 g/g) and comparatively lesser impurities (byproducts) were achieved with 57 g/L initial lactose concentration. The batch growth kinetics was eventually used to develop and test a mathematical model for propionic acid fermentation by P. acidipropionici at pH 6.5 and S-o = 57 g/L. Y-X/S(max) was found to be the most sensitive parameter of the model. The same model also successfully simulated the batch kinetics observed at S-o = 37 g/L. However the model failed to simulate the fermentation kinetics observed at S-o = 73 g/L. The developed model can be used for process optimization studies.