Lipase from candida rugosa was immobilized in a freeze-dried polyvinyl alcohol (PVA) matrix for investigating the enzymatic reactivity. This matrix was prepared in a microreactor to achieve continuous enzymatic reactions. The performances of the lipase immobilized microreactors were compared in terms of the micro channel type and the reaction conditions. The freeze-dried matrix made in the microchannel possessed porous microstructure with 2-20 !m of well-aligned pores. These pore structures were obtained as a replica of the ice crystals formed during the freezing stage. Experiments suggested that the enzymatic reaction with the immobilized lipase was a diffusion controlled system. It was found that the present microreactors exhibited approximately 10 times higher reaction performance than the large scaled plug flow reactor with the freeze-dried specimens. The freeze-dried microstructure fabricated in a microspace had a significant effect of improving enzymatic reactions. A solution flow in the microchannel is under an influence of both the porous microstructure and the channel structure. When the channel size was smaller than 1000 !m, the flow regime would mainly be controlled by the freeze-dried microstructure.