In this paper, large eddy simulation of a two-dimensional spatially developing transitional free methane diffusion jet at moderate Reynolds number is performed. The solver of the governing equations is built based on a projection method and time integration is carried out using a second-order Adams-Bashforth scheme. A dynamic eddy viscosity model is utilized for the turbulent subgrid scale terms and a similar dynamic method is applied for modeling the filtered reaction rate. The direct solver for pressure correction Poisson equation is based on the Buneman variant of cyclic odd-even reduction algorithm. A reduced four-step chemical kinetic mechanism is applied for the simulation of methane combustion. Ignition process is well described by the simulation. Detailed description of transient vortical structures in the entire flow field is given along with transient vortex-flame interactions. The development of a diffusion jet flame is found to involve two distinct phases of "turbulence dominated" and "reaction dominated" respectively. The "turbulence dominated" phase exists only for a very short time at the initial stage of the flame. (C) 2003 Elsevier Ltd. All rights reserved.