Alternative fuels such as LPG, CNG, hydrogen etc. have emerged as solutions to address depleting crude oil resources as well as deteriorating urban air quality. As a gaseous fuel, LPG has already been proven in terms of low emissions of carbon monoxide and hydrocarbon. The Government of India has taken an important and encouraging step towards the reduction of atmospheric pollution by directing its attention towards use of LPG as an automobile fuel. On Indian roads it has been found that, the vehicles that run on LPG have low compression ratio. It was also found that LPG could be directly retrofitted in existing gasoline fuelled engine and hence operating parameters such as compression ratio and ignition timing might affect performance and exhaust emission. So, the present work performed experiments to study the performance and emission characteristic of LPG fuelled SI engine at different compression ratios such as 9,10,11,12 and at ignition timing 10°BTDC, 20°BTDC, 30°BTDC and 40°BTDC. A single cylinder, 4-stroke, water-cooled, diesel engine converted to operate in SI mode was used; an arrangement was made to vary compression ratio and ignition timing. The results obtained shows that the engine running on an LPG fuel system has low brake thermal efficiency (4% - 10%) at lower compression ratio as compare to gasoline fuelled engine. But at higher compression ratio it was found to be increased in the range 13.18% to 40.78%. The CO (40% - 70%) and HC (70% - 80%) were found to be much lower as compared to gasoline fuelled engine.