Laminar forced convection inside trapezoidal duct is of interest in design of thermal equipment. Heat transfer to both hydrodynamically and thermally developing three dimensional forced convection inside a duct having trapezoidal cross section was investigated numerically under steady-state and constant surface temperature conditions. Numerical study was carried out for Reynolds number range of 100 <= Re <= 800. Air (Pr congruent to 0.7) was used as working fluid. Numerical solutions were obtained using commercial CFD code Ansys Fluent 6.3.26. The average Nusselt numbers and friction factors were presented as function of Reynolds numbers. Local Nusselt numbers and Fanning friction factors were also plotted as function of position along the duct. Velocity and temperature contours were presented at different positions along the duct.