Solid cellulose-based radioactive wastes (CBW) constitutes in some cases, about 70% of the total solid low and intermediate level organic wastes originated from peaceful applications of nuclear technology in various fields of our life. Cesium-137 and cobalt-60 represent two of the most important radioisotopes spiking these waste categories. Both are serious contamination concerns due to their high energy gamma ray emitting (Cs-137 = 0.662 MeV and Co-60 = 1.17 and 1.33 MeV), besides 137 Cs is considered as one of long-lived isotopes (T 1/2 = 30.5 years). In this part of work, laboratory scale attempts were performed to follow bioaccumulation of Cs-137 and/or Co-60, found separately or together in a mixture of some solid CBW simulates. The process is based on the capability of Pleurotus pulmonarius to biodegrade the solid CBW simulates achieving acceptable weight reduction for the waste as well as reasonable bioaccumulation of the two isotopes from the spiked mixture, within their cells. Up to 134.95 and 41.1 kBq/kg (based on the dry weight of mushroom) were accumulated from Cs-137 and Co-60 respectively within a period of 54±3 days. It is worth mentioning that more than 54% weight reduction percent for the solid CBW simulates was acquired only due to a single cultivation process. Based on the data so far obtained, the bioremediation process for solid CBW based on the P. pulmonarius bioactivity seems to be simple, effective, and economical and can work where the other process cannot be applied.