Natural Chlorella has unique physicochemical/biological properties. An eco-friendly composite material was prepared by thermo-chemical modification of Chlorella with citric acid and used as drug release carrier for ketoprofen. The structure and morphology of the synthesized citric acid-Chlorella composites were characterized by FT-IR and SEM, respectively. The surface properties such as carboxyl content, esterification rate, and isoelectric charge point of the composites synthesized at different reaction temperatures were studied, and 140 °C is determined as the optimal reaction temperature The composite prepared under this condition has the maximum water absorption multiplicity of 35.8 g/g and exhibits a sensitivity to pH of swelling medium. The drug loading performance of citric acid cross-linked immobilized Chlorella vulgaris composites and the slow release performance under simulated in vivo environment were investigated using ketoprofen as template drug. The results show that the cumulative release rate of ketoprofen after 8 h is 93.8 % and 79.7 % at pH=1.2 and pH=6.8, respectively, and the polymer has a slow release effect on anti-inflammatory drugs with potential applications.