Declining petroleum sources and increasing demands for energy and emissions characteristics of fossil fuels combustion lead investigations to clean, available and low-cost energy resources. Dual-fuelled diesel engine by NG as main fuel and biodiesel blend as pilot fuel can be an appreciate idea to reduce engine emissions and using renewable source of fuel. The main aim of present study is to use the blend of glycerol triacetate (GT) additive and biodiesel to reduce emissions and to improve fuel cost of dual-fuelled diesel engine by natural gas as main fuel. Tests performed on dual fueled, constant speed (1500 rpm) diesel engine by two levels of biodiesels (B5, B20) with three levels of GT additives (3%, 5%, 7%) and neat diesel fuel as pilot fuel and four levels of pilot fuel to gaseous fuel (20%, 30%, 40%, 50%). Based on results, using B5A3 as pilot fuel decreased NOx emission by 24% in pilot-to-gaseous (P/G) fuel ratio of 50%. Using B20A3 as pilot fuel significantly reduced PM emission, such that in P/G ratio of 20% it was 85% lower than that of diesel as pilot fuel. CO emission was found to be 72% lower than that of diesel as pilot fuel in case of using B5A7 as pilot fuel in P/G ratio of 20%. Using B5 as pilot fuel in P/G ratio of 20% reduced CO2 emission by about 8% compared to that of diesel as pilot fuel. UHC emission had been increased slightly using biodiesel and GT additive rather than diesel pilot fuel. It was also observed that in the P/G ratio of 40% using B5 fuel, the GP cost was 0.22 $/kWh which is about 15% lower than that for diesel pilot fuel.