Bioethanol is mainly produced by sugar fermentation process. Due to global demand on energy for transportation and environmental concern, biofuels as renewable energy in replacing petrol, the non-renewable energy source, has come into picture. Utilization of lignocellulosic biomass such as woody biomass (trees), herbaceous biomass (grasses) and waste cellulosic materials (solid waste) could be used in replacing starch (such as corn and potato) as source of sugar in producing bioethanol. Recently, study on cellulosic ethanol was focussing on fermentation process using ethanologenic strain such as engineered Escherichia coli and Saccharomyces cerevisiae. Invasive method in the study during fermentation may lead to uncertain or unwanted screening strategies or metabolic pathways. This paper reviews about the online monitoring system used by researchers in order to study the growth kinetics of ethanologenic strain. Online monitoring system for the Oxygen Transfer Rate (OTR) and Carbon dioxide Transfer Rate (CTR) is found to be the important method to study kinetic model of ethanologenic strain, thus increasing metabolic yields with optimum design condition.