Abstract: A simple identification based on the OUR (oxygen uptake rate) is proposed to rise above the difficulty of on-line classification of mycelia growth phases in aerobic fermentation process. The specific growth rate at a certain growth phase is pre-estimated using the on-line measurable OUR, then the on-line identification of growth phases is available to carry out in accordance to the pre-estimated value of specific growth rate. Such an identification is very easy to implement since the OUR can be obtained on-line. This method has been applied to Nosiheptide fermentation process, and the identification results are consistent with the actual process. It will not only deepen the understanding of the present situation of production, but also guide the timely implementation of various control schemes to improve the quality of products.