The invention relates to medicine and concerns a photosensitizer for detecting and curing tumors. The inventive photosensitizer is embodied in the form of a composition containing chlorin in the form of salt and alkali metals. The chlorin is composed of 80-90% of chlorin e.sub.6, 5-20 of purpurin 5 and the rest being purpurin 18-chlorin p.sub.6. Said photosensitizer is produced by extracting Spirulina biomass with the aid of acetone. Afterwards said biomass is exposed to acid treatment, neutralization, hydrolysis, extraction of pheophorbide a, dissolution in acetone, addition of a strong base, neutralization and reprecipitation of chlorin e.sub.6.