In this study, the biodiesel obtained from the waste olive oil by transesterification method has been mixed with a 30% of diesel fuel as volume and tested with a single cylinder direct injection diesel engine. The main purpose of this study is to obtain purer biodiesel from waste olive oil using methyl alcohol (CH3OH) and sodium hydroxide (NaOH) as catalyst in the transesterification method and research performance, combustion and emission characteristics in detail in a direct injection diesel engine. The combustion, engine performance and exhaust emission values have been also compared with diesel fuel. The test engine was operated at a constant speed of 2200 rpm and different engine loads such as 3.25 Nm, 7.5 Nm, 11.25 Nm, 18.75 Nm. According to the experimental results, the thermal efficiency of biodiesel is lower by about 1% to 5% than diesel. CO is lower about 37.5 % with biodiesel than that of diesel at 18.75 Nm. CO2 is higher 41% with biodiesel than diesel at 11.25 Nm. NOx was measured 9.5% higher than diesel fuel at 18.75 Nm. Soot emissions decreased by 37.5% compared to diesel.