The present study numerically investigates the hydrodynamic and thermal characteristics of single phase pressure driven flow for a single square microchannels using Lattice Boltzmann method (LBM). Two dimensional and nine directional model (D2Q9) in Lattice Boltzmann method is used to simulate the flow and water is considered as the working fluid. Uniform temperature is assumed at the channel walls and the fluid temperature is taken to be lower than that of the wall. Hydrodynamic and thermal entrance lengths are determined using Lattice Boltzmann method for different Reynolds numbers (5, 10, 50 and 100). The results obtained are compared with the available experimental μ-PIV studies and thermal studies in literature and found to be consistent.