Vegetable oils are renewable fuels that offer reductions in carbon dioxide emissions, and a number of studies have been conducted with vegetable oils in diesel engines. This study investigated rapeseed oil blended with light fuel oil as a diesel fuel substitute. The spray characteristics, such as spray angle and penetration under high pressure and room temperature conditions (1.57 MPa and 298 K), are discussed for fuel injection rates measured by the Bosch long tube method. The performance and emissions of a small, single-cylinder, DI diesel engine equipped with a toroidal type combustion chamber and a multiple-hole nozzle of 4-φ0.2 were also examined. Blended fuels with equal proportions of light fuel oil and rapeseed oil, as well as fuels with lower rapeseed oil ratios, showed spray characteristics as good as those for light fuel oil alone. It was found that unblended rapeseed oil has a lower injection rate than that of light fuel oil. Compared with light fuel oil operation, equal proportions of light fuel oil and rapeseed oil showed quite similar brake specific energy consumption (BSEC) and combustion characteristics, and demonstrated lower smoke emission.