Abstract: Objective To investigate the role of alginate-polylysine-alginate (APA) microcapsules in protecting rat islet cells in cryopreservation. Method Purified rat islet cells microencapsulated with APA and free islet cells were cryopreserved for one month and then thawed for culture in RPMI1640 overnight. The morphology of the cells was observed and their function assessed by stimulated insulin release test. Result APA microcapsulation protected the fragile islets from freezing damage by increasing the recovery rate of the cells from 68.6%±2.9% to 94.7%±1.4% (P<0.05). After incubation with high glucose (16.7 mmol/L) solution, the insulin release from the encapsulated cells after cryopreservation significantly increased in comparison with that of the nonencapsulated cells (22.6±1.8 mU/Lvs 11.7±1.5 mU/L, P<0.05). In high glucose solution containing theo-phylline, the calculated stimulation index of the encapsulated cells was about 3 times that of the nonencapsulated cells. Conclusion APA microencapsulation may significantly increase the post-thaw recovery and improve the function for cryopreserved rat islets.