Emission from diesel engine has been considered as major air pollution sources. The blending of feedstocks is motivated by property enhancement and cost reduction. In this study rubber seed/palm oil mixture at equal blend ratio was used to produce biodiesel. Parametric effect on trans esterification were studied using response surface methodology (RSM). Maximum yield was determined. Methyl ester at optimized condition was produced. Thermo physical properties were studied. Methyl ester effect on the emissions and performance of unmodified indirect injection diesel engine (IDI) at full load was examined. The results show that blends torque and brake mean effective pressure (BMEP) were 1.1 and 1 lower. Compared to diesel fuel, power and brake thermal efficiency (BTE) were 1.1 and 1.3 lower, but brake specific fuel consumption (BSFC) was 1.4 higher. The CO was reduced 2 while CO2, NOx and exhaust temperature increased on averages of 1, 1.2 and 1.1 respectively. © 2006-2016 Asian Research Publishing Network (ARPN). All rights reserved.