In this study, heat release rate (HRR) characteristics of natural-gas (NG) dual-fuel (DF) engine using biodiesel pilot fuel were investigated by stochastic reactor model (SRM). SRM Engine Suite software having solution method in zero-dimensional was used to apply stochastic reactor model into the DF engine. Results of the study were validated by the experimental data obtained from biodiesel pilot fuelled NG engine. Biodiesel surrogate fuel was considered as a mixture of methyl decanoate (25 v%), methyl-9-decenoate (25 v%) and n-heptane (50 v%) and its skeletal kinetic mechanism includes 71 species and 217 reactions. In addition, it is shown that biodiesel surrogate fuel chemical kinetic mechanism could represent soy biodiesel fuel. Case studies were realized under 50, 100, 150 and 200 stochastic particles with 120 MPa pilot fuel injection pressure and 17°BTDC pilot fuel injection timing conditions in the simulations. It was observed that SRM method is a good tool to investigate HRR of biodiesel pilot fuelled DF engine.