Biomaterials that support vascularization without activating immune competent endothelial cells are desirous in immunoisolation. The aim of the present study was to evaluate effect of chitosan-alginate membrane on adhesion and activation of endothelial cells. The AFM photographs showed that the CS/ALG membrane surface roughness values were less than CS membrane and ALG membrane. The contact angle of CS/ALG membrane was between ALG membrane and CS membrane. The surface roughness and hydrophilicity of CS/ALG membrane affect the adhesion and activation on endothelial cells. The CS/ALG membrane did not allow the majority of cells to adhere well but maintained their viability. The membrane leach-outs were nontoxic to the cells, as confirmed by tetrazolium reduction (MTT) and trypan blue assays. The growth curves of the endothelial cells desquamated from the CS/ALG membrane suggested that the endothelial cellsmaintain their activation. Taken together these results point out that CS/ALG membrane is compatible with endothelial cells and maintains their nonactivated status. (c) 2008 Elsevier B. V. All rights reserved.