The uptake of the fungicide, thiabendazole (TBZ) on a sawdust medium by fruit bodies of the oyster mushroom, Pleurotus ostreatus (JACQ. ex FR.) KUMM. was investigated. The medium was treated with the fungicide at concentrations of practical use (Exp. 1), or at concentrations of 10 times (Exp. 2) and 50 times (Exp. 3) as much as that of Exp. 1. The fruit bodies, mycelia, and media were sampled at intervals after cultivation on the media. The residual analysis of TBZ was conducted by high-performance liquid chromatograph with a fluorimetric detector. The fungicide was detectable in all fruit bodies of the oyster mushroom collected from all TBZ-treated samples, showing that it transferred to the fruit bodies from the media. The amount of TBZ in fruit bodies from Exp. 1 was less than the tolerance level for TBZ residue in foods specified by the Environmental Agency, Japan. Moreover, no difference of TBZ concentrations in fruit bodies was observed among samples collected at the first and second flushes, although the TBZ concentration in the pilei was two to four times as much as that of the stems. The yield and quality of fruit bodies of the oyster mushroom decreased slightly in Exp. 2 and markedly in Exp. 3.