This paper deals with the modelling of substrate inhibition in microbial growth processes. For successful applications and over all model validation in microbial growth processes, a new substrate inhibition model, modified Aiba model, has been introduced. Performances are compared on the basis of the goodness of fit, the parameter sensitivity analysis, and the best-fittings of different experimental data in the literature, respectively. Finally, the modified Aiba model turns out to be a very simple but flexible enough model structure for representing the microbial growth kinetics with limited number of parameters.