Five experiments were performed to determine the importance of chitin and cellulose in the diet of juvenile <em>C. sapidus</em>. A compartmentalized recirculating system was established to provide optimal conditions, maintaining the animals with little mortality. The appropriate ration, compartment size, and an adequate baseline diet were established. We replaced 20% of a commercial diet with varying amounts of chitin and cellulose. Crabs fed the cellulose-containing diet had higher growth rates, conversion efficiencies, molt increments and frequencies than crabs fed the chitin-containing diet, but were equal to the control diet. We then assayed for chitinase and cellulase in gut tissues. Chitinase had lower specific activity (0.072 + 0.159 mU mg-1min-1) than cellulase (3.52 + 0.16 mU mg-1min-1) in the foregut and hepatopancreas. There was no effect of diet on specific activity. The results show juvenile <em>C. sapidus</em> is capable of utilizing cellulose, but not chitin, when delivered as 20% of a diet.