An experimental investigation was made on heat transfer and pressure drop using a spacer in a rectangular channel, and the basic characteristics of the spacer were obtained. These included the local heat transfer coefficient and static pressure drop distribution. A heat transfer enhancement was caused by the effect of turbulence at the spacer outlet region, not as the effect of increased velocity in the spacer ; and then the flow diffusion and contraction around the spacer caused a larger pressure drop. Four dimensionless parameters were defined as spacer specifications : blockage ratio ε, gap ratio α, spacer length ratio β, and spacer existence ratioθ. Among the parameters, blockage ratio ε had the most influence on performance enhancement. The total performance between heat transfer and pressure drop were estimated under the condition of a constant fluid transportation power. The spacers with blockage ratio ε=0.5 and spacer existence ratio θ=0.2 gave excellent performances.