Lovastatin production using pellets of Aspergillus terreus was investigated in an airlift reactor. A fuzzy system has been developed for predicting the lovastatin productivity. Analysis of the effect of dilution rate and biomass concentration on the productivity of lovastatin was carried out and hence these were taken as inputs for the fuzzy system. The rule base has been developed using the conceptions of developmental processes in lovastatin production. The fuzzy system has been constructed on the basis of experimental results and operator’s knowledge. The values predicted for lovastatin productivity by the fuzzy system has been compared with the experimental data. The R squared value and mean squared error has been calculated to evaluate the quality of the fuzzy system. The performance measures show that the rule-based results of the fuzzy system is in accordance with the experimental results. The utilization of fuzzy system aided in the increase of lovastatin productivity by about 1.3 times when compared to previous empirical experimental results.