the objective of this study was to determine the effective gamma ray radiation to decontaminate the soft extract from rhizophora mangle l. (red mangrove) bark. three batches of this active ingredient, dried in a spray dryer and irradiated in a gammacell-5000 equipment at a dose rate of 6.26 kgy/h, were obtained. similarly, three doses (3, 5 and 8 kgy) were evaluated. the irradiating process was controlled by means of ceric sulphate dosimeters. the microbial limit and the content of tannins were determined for each batch of the active ingredient irradiated at the various tested doses. on the basis of the final results, there was reduction of two logarithmic development cycles of the irradiated batches at 5 and 8 kgy doses, when compared with the initial polluting load. the tannin concentration of irradiated batches was kept within the specified limits and no differences were found between the treated batches and the untreated product. the decontamination dose for the dried active ingredient from red mangrove was set at 5 kgy. in this way, it is possible to guarantee a suitable product for obtaining new pharmaceutical preparations.