The effects of high boiling point fuel additives on deposits were investigated in a commercial turbocharged direct injection gasoline engine. Three additives, that the boiling points are 190-196 ℃, were examined. The additives are C11 aromatic hydrocarbon, C6 diamine and N-methyl-aniline (NMA). The basic gasoline has no detergent, premium grade, i.e., about 100 RON. Tested gasolines were prepared by blending with the each additive of volumetric 10% and the basic one. The end points of test fuel distillation temperature were elevated about 15 ℃ from that of the basic gasoline by the addition of those additives. The engine operation condition for the deposit growth was the engine speed of 1600 rpm, the brake mean effective pressure of about 0.7 MPa using the Atkinson cycle, and stoichiometric air/fuel ratio. It was found that the amino group additives increase the deposits extremely. The piston top deposit thickness, after operating the deposit growth of 30 hours, on the fuel consumption of about 200 L, was NMA, C11 aromatic, and basic (no additive), in descending order. The piston top deposit thickness in the C11 aromatic blend was about twice of the basic, and that in the NMA blend was about four times of the basic. C6 diamine blend was resulted compression leakage on the fuel consumption of 10 L, because the piston rings stuck to the grooves. The deposit growth mechanisms should be considered from some chemical analyses.