AbstractA block copolymer, (short‐chain alginate)‐co‐MPEG, was synthesized and used for coating the capsular membranes of the photosensitive microcapsules. The resulted microcapsules exhibited an excellent mechanical strength. The permeability test results revealed that the capsular membrane was freely permeable to cytochrome C and myoglobin, less permeable to serum albumin, and almost impermeable to IgG. In the cell attachment test, the results showed that the surface formed by (short‐chain alginate)‐co‐MPEG copolymer could effectively reduce cell adhesion as compared to poly(L‐lysine) and alginate. The microcapsules were evaluated by intraperitoneal implantation experiment of mice. The results demonstrated that microcapsules coated with (short‐chain alginate)‐co‐MPEG were more biocompatible than the conventional alginate/PLL/alginate microcapsules. © 2001 Wiley Periodicals, Inc. J Biomed Mater Res 59: 118–126, 2002