Synthesis gas of H-2/CO = 2/1 was obtained from Japanese cedar chips at a gasification efficiency of 93%, by using steam as a gasification agent at a gasification temperature (T (g)) of 1,173 K. Carbon dioxide inevitably contained in biomass-derived synthesis gas did not affect the Fischer-Tropsch synthesis (FTS) reaction. In contrast, trace amount of sulfur impurity in the gas gave rise to fatal deactivation of Ru-based FTS catalysts under the reaction conditions of T = 503 K, P = 1 MPa, and W/F = 2-10 g-catal. h/mol, indicating that complete desulfurization of the gas to < 1 ppm was prerequisite in order to obtain stable FTS activity. With increasing impurity levels of H2S, selectivity for higher hydrocarbons decreased.