The suitability cattails weed botanical fractions namely, stems and leaves (SL), spikes (SP), rhizomes and roots (RR) and whole cattail weed (WCW) as substrates for growing two oyster mushrooms was investigated at three spawn rates 1%, 1.5% and 4% on wet substrate weight basis using plastic bag technology cultivation under local conditions. Amongst data collected were yield, biological efficiency (BE), crop period, mushroom number and size. Maximum mushroom yield (297g/kg wet substrate), biological yield (826 g/kg dry substrate) were obtained in WCW at spawn rate of 4% for Pleurotus HK-37. In Pleurotus sapidus maximum mushroom yield (239 g/kg wet substrate) and biological yield (1027 g/kg dry substrate) were obtained from WCW and RR, respectively at 1.5% spawn rate. A maximum BE (101%) was obtained when Pleurotus HK-37 was grown on RR at spawn rate of 4%. Conversely, maximum BE (103%) for Pleurotus sapidus was obtained in RR at spawn rate of 1.5%, followed by (66%) in WCW at same spawn rate. The study recommends WCW as a new substrate for cultivation of Pleurotus HK 37 at spawn rate of 4% and Pleurotus sapidus, at spawn rate of 1.5% under local conditions, which is being reported for the first time in Tanzania.