A tubular batch micro-reactor system was used for hydrothermal gasification (HTG) of Cladophora glomerata (C. glomerata) as green macroalgae found in the southern coast of the Caspian Sea, Iran. Non-catalytic tests were performed to determine the optimum condition for hydrogen production. Hydrochar, as a solid residue of non-catalytic HTG was characterized by BET, FESEM, and ICP-OES methods to determine its physiochemical properties. Surface area and pore volume of C. glomerata increased drastically after HTG. Also, the aqueous products were identified and quantified by GC-MS and GC-FID methods. Hydrochar was loaded to the reactor to determine its catalytic effect on HTG. HTG was promoted by inorganic compounds in the hydrochar and its porosity. The maximum hydrogen yield of 9.63 mmol/g was observed in the presence of algal hydrochar with the weight ratio of 0.4 to feedstock. Also, acids production was inhibited while phenol production was promoted in the presence of hydrochar. (C) 2016 Elsevier Ltd. All rights reserved.