In this study, the possibility of using tea production waste as a new casing material in mushroom (Agaricus bisporus) cultivation was investigated. Some physical and chemical characteristics of tea waste, fermented tea waste and a mixture of tea waste with peat were compared with that of peat casing, as were their effects on yield. The highest yield was obtained from peat casing. Using tea production waste alone as a casing was not acceptable for assured yield when it was compared with peat. But, a mixture of tea production waste with peat in 1:1 (v:v) ratio increased the yield. There was no significant difference between the mushroom yields of tea production waste + peat and peat casing materials at the end of 30 and 40 days. High salt content, organic and inorganic compounds in casing materials caused reduction of yields. However, a high iron content in casing material gave a significant positive correlation with total yield at 40 days.