The fermentation kinetics of an extracellular antibiotic, actinorhodin, by Streptomyces coelicolor were studied in a batch system. A simple model was proposed using the Logistic equation for growth, the Luedeking-Piret equation for actinorhodin production and Luedeking-Piret-like equations for glucose and oxygen consumptions. The model appeared to provide a reasonable description for each parameter during the growth phase.