This numerical study aims to investigate the effects of a horizontal baffle on the heat transfer characteristics of pulsating opposing mixed convection in a parallel vertical open channel. The influences of the dimensionless pulsating frequency Stroubal number and magnitude A, Prandtl number and baffle position L-b on the velocity and temperature distribution and long-time average Nusselt number < Nu > variation for the system at various Re and Gr/Re-2 are explored in detail. Our results show that the channel with both flow pulsation and a baffle gives the best heat transfer. With a larger Re, the inlet flow pulsation dominates the whole velocity field in the channel. (Nu) always increases with a larger Re, pulsation magnitude A and Prandtl number. Maximum < Nu > occurs at some specific imposed pulsating frequencies which can be considered to be the natural frequency of the system. (c) 2005 Elsevier Ltd. All rights reserved.