The amylase, cellulase and proteinase enzyme from the stomach and intestine of the Mekong Giant Catfish that had been fed with various diets consisting of Spirulina, were studied at pH 2-12 and at temperatures between 25-80ºC. This study found that; amylase activities of the stomach were alkaline amylase and the optimal temperatures to be 25 and 50ºC. Amylase activities of the intestine were neutral amylase as well as alkaline amylase and the optimal temperature range was at 25-30ºC. The cellulase activities were acidic cellulase and alkaline cellulase in both the stomach and the intestine. In the stomach, the acidic cellulase showed the optimal temperatures to be at 30, 40 and 50ºC, however alkaline cellulase were 30 and 50ºC. In the intestine, acidic cellulase showed the optimal temperatures to be at 25, 60 and 70ºC and the alkaline cellulase to be 80ºC. For proteinase activity, the stomach was acidic proteinase and alkaline proteinase, but the intestine was alkaline proteinase. The acidic proteinase activities of the stomach showed the optimal temperatures to be at 40, 50 and 60ºC and the alkaline proteinase activity proved to be at 40, 60 and 70ºC. The optimal conditions for amylase enzymes showed the higher specific activity in the intestine than in the stomach including the proteinase enzyme. At room temperature (25-30ºC), amylase and proteinase specific acitivity dominated in the intestine, while cellulase specific activity dominated in the stomach.