The feed rate optimization of fed batch cultures with two or more feed rates is a numerically difficult problem involving two or more singular control variables. Even when implicit or explicit forms of singular control profiles can be derived, the sequence of control including bang-bang regions and singular regions must be known a priori. Thus, no attempt has been reported in literature.A nonsingular transformation algorithm has been proposed to convert singular control problems with control variables into nonsingular problems involving nonsingular control variables. Using the proposed transformation and numerical technique, optimization of fed-batch cultures with two feed rates has been carried out succesfully.