Biodiesel is an environmentally friendly and a renewable alternative diesel fuel that can be used in diesel engines with little or no modification. Used frying oil is one of the raw materials which can be used for biodiesel production. The objective of this study was to investigate the effects of used frying oil originated from biodiesel on engine performance and emissions in a Fiat Doblo 1.9 DS, four-cylinder four-stroke, 46 kW power capacity diesel engine. Comparative measurements with no. 2 diesel fuel were conducted on both engine power and emission characteristics of each of the fuel used. Biodiesel, when compared to no. 2 diesel fuel, showed reduction in wheel force over 3.35% and it also reduced the wheel power by over 2.03%. In the acceleration tests, 40-100 km/h and 60-100 km/h acceleration periods were measured and a reduction of 7.32% and 8.78% were observed, respectively. According to emission tests, as a result of biodiesel consumption, a reduction of 8.59% in CO emission and an increase of 2.62% were observed in CO2 emission. Also, NOx emissions increased by 5.03% as a result of biodiesel consumption. HC emissions and particulate emissions have a significant effect on air pollution. As a result of biodiesel usage, HC and particulate emissions decreased by 30.66% and 63.33%, respectively. When the fuel consumption amounts are compared, it was observed that biodiesel consumption was 2.43% less than that of no. 2 diesel fuel. These emission engine test results show that biodiesel is a more environment friendly fuel than no. 2 diesel fuel.