To produce hydrogenated amorphous carbon (a-C:H) films with high mass density at a high deposition rate and low substrate bias voltage, we deposited these films on a Si substrate by plasma chemical vapor deposition, using toluene as a source compound and varying the gas flow-rate ratio of H-2/(H-2+ Ar). By decreasing the gas flow-rate ratio from 55% to 11%, the hydrogen content in the films decreased, and the density of sp(3) carbon atoms in the films increased, whereas their surface roughness increased. At the gas flow-rate ratio of 11%, we produced a-C:H films with a high bulk density of 1830 kg/m(3) at a high deposition rate of 81.1 nm/min.