In this study, an experimental investigation was presented to determine the effects of various ratios of Liquefied Petroleum Gas (LPG), containing 30% propane and 70% butane, on the performance and exhaust emission in a dual fuel engine with direct injection. The tests were performed at maximum torque speed of 2600 rpm with a various loads of maximum torque (20%, 40%, 60%, 80% and 100%) by using pure diesel fuel or dual fuel containing 20%, 40%, 60%, 80% and 90% of LPG. The test results showed that the smoke and Nitrogen oxide (NOx) emissions decrease, while carbon monoxide (CO) and hydrocarbon (HC) emissions increase at all mixtures of LPG and diesel fuel. Brake specific fuel consumption (bsfc) decreases by 3.5-15% with 40% LPG while the load increases. Exhaust gas temperatures at the mixture fuel were lower than that of diesel fuel in general. It was concluded that LPG can be used with diesel fuel as a mixture up to 40-60% of LPG, provided that CO and HC emissions can be lowered.