This dissertation work addresses the suitability of fly ash and pond ash for stowing in underground coal mines. The sand stowing operation is becoming practically infeasible day by day due to severe dearth of river sand which is considered as a primary stowing material. Due to scarcity of river sand, the mining companies face a lot of problems in stowing their underground mines. As a result, the voids created due to excavation of coal/mineral in most of the underground mines are not properly stowed and left unfilled which is responsible for surface subsidence. It is recognized that fly ash/pond ash is a major alternative to river sand as a stowing material and can solve the above mentioned problems. Therefore, the properties of fly ash/pond ash should be studied in depth before hand for assessing their suitability for stowing. In this investigation, the characteristics of total 16 numbers of Class F fly ash and pond ash samples collected from two thermal power stations namely, Talcher Thermal Power Station (TTPS) and Talcher Super Thermal Power Station (TSTPS), Kaniha are studied for assessing their suitability for stowing in the nearby underground coal mines. The study of physico-chemical and engineering properties revealed that the fly ash and pond ash samples of both the power stations are suitable for stowing. It is observed that the fly ash and pond ash particles are almost spherical in shape. Comparatively, the pond ash samples are coarser in size and possess higher coefficient of permeability than the fly ash samples and therefore, better for stowing. However, the TSTPS pond ash samples are much coarser in size and highly permeable than the TTPS pond ash samples and most suitable for stowing. It is also found that the pond ash possesses higher water holding capacity (WHC) as compared to the fly ash, which absorbs higher quantity of water and allows less drainage after stowing. It will definitely help in reducing the pumping cost.