Objective To investigate the biocompatibil ity of sil ica gel embedded permanent magnets of themicturition alert device dedicated to neurogenic bladder. Methods According to the national standards of biologicalevaluation of medical equipment (GB/T 16886), Shanghai Biomaterial Research and Test Center was confided to evaluate the biocompatibil ity of sil ica gel embedded permanent magnets both in vitro and in vivo, including cytotoxicity test, sensitization test, primary skin irritant test and acute general toxicity test. The cytotoxicity test was performed according to the agar diffusion method. The L929 cell discoloration index and cell lysis index were counted at 24 hours after the action of the specimen. The sensitization test was performed according to the maximal dose method. The skin response was evaluated in 30 male albino guinea-pigs at 24 and 48 hours after the routine induction and provocation of leaching l iquors of the specimen. The primary skin irritant test was evaluated in 2 male healthy New Zealand rabbits according to the local tissue response at 24, 48 and 72 hours after intradermal injection of leaching l iquors of the specimen. The acute general toxicity test was evaluated in 10 male Kumming mice musculus albus according to animal condition at 4, 24, 48 and 72 hours after injection of leaching l iquors of the specimen through the caudal vein. Both the general reaction of canines and the pathology of the local bladder walls were observed at 2, 4 and 8 weeks after a permanent magnet was fixed on the anterior wall of urinary bladder in three canines. Results No sensitization, no stimulation and no acute general toxicity were observed except sl ight cytotoxicity to sil ica gel embeddedpermanent magnets. After implantation of a permanent magnet, the canines showed excellent tolerace, which manifested as no abnormal ity in spirit, appetite, urine and stool, healed wounds and no infection. Adhesions occurred between the epiploon and the bladder wall around the permanent magnet in two canines at 2 and 4 weeks, and between the lower abdominal wall and the bladder wall around the permanent magnet in the other canine at 8 weeks. The local bladder wall below permanent magnet was thickened, the fibrous capsule around the permanent magnet was thin, but the bladder mucosa was normal. Inflammatory reaction such as congestion, edema and inflammatory cells lessened from the serosa layer to the mucosa layer microscopically. Conclusion Sil ica gel embedded permanent magnets used in the micturition alert device dedicated to neurogenic bladde has excellent biocompatibil ity and meet the criteria for cl inical appl ication．