This paper presents results on the production of alpha -agarase by a fermentation process and its separation using membrane microfiltration (MF). Optimization of fermentation conditions for alpha -agarase production using Altermonas agarlyticus grown on medium containing agar as a carbon source was done in batch, fed-batch and continuous fermentations. Continuous culture at a dilution rate of 0.03 h(-1) appeared to be best suited for production of alpha -agarase by this organism. Al 0.03 h(-1) dilution rate, enzyme activity was 0.9 U/ml. Clarification of broth was done using a hollow-fibre microfiltration membrane. The influence of hydrodynamic parameters on permeate flux and enzyme activity was studied. The best performance was obtained with prefiltered fermentation broth. A stable permeate flux of about 250-270 ml/min.m(2) and an enzyme retention rate between 0% and 25% was obtained at temperatures between 6 degreesC and 22 degreesC, transmembrane pressure of 100 mm Hg and fluid cross-now velocity of 4 x 10(-2) m/s. From the experiments on concentration of fermentation broth, the best compromise between enzyme activity transmission and permeate flux was obtained at a concentration factor of 2.