We report herein the production of H-2 and CH4 from the catalytic hydrothermal gasification of microalgae. All reactions were performed at 430 degrees C for 1 h using a batch reactor. The effects of catalyst, water density, and initial feedstock on the mole fractions and yields of H-2 and CH4 were examined. The catalytic yields of H-2 and CH4 increased 2-3 and 3-9 times higher than their yields without catalysts, respectively. Pt/C and Ru/C catalysts produced the highest mole fractions and yields of H-2, which were 43.11% and 5.75 mmol/g and 42.01% and 5.97 mmol/g, respectively. In contrast, Pd/C and Rh/C catalysts produced the highest mole fractions and yields of CH4, which were 35.24% and 6.17 mmol/g and 31.39% and 7.19 mmol/g, respectively. When the water density was increased, the H-2 content in the gaseous products decreased, and the H-2 yield initially increased and subsequently decreased the peak value. The mole fraction and yield of CH4 always increased with increasing water density, indicating that the methanation reaction preferentially occurs at high water density. Fatty acids derived from algae contributed to the production of CH4. Protein and carbohydrate-based feedstocks preferentially produced H-2. A synergistic effect was observed among the biochemical components of algae during the gasification of algae.