A study was carried out in Mardi watershed, Nepal, to estimate stem volume and biomass of the different forest types: Mixed Hardwood Forest (MHF) with Schima wallichii and Castanopsis indica as dominant species; Oak ( Quercus ) Forest (OF); and High Mountain Mixed Forest (HMMF) with Rhododendron species, and to analyse the factors that influence their variations. The per hectare stem volume and biomass of trees in HMMF and OF was 2 to 3.5 times higher than that of MHF. MHF, which is the most accessible forest in the conservation area, has slightly higher mean volume and about double the stem density compared to the forests in the hilly areas. The state of forests in the conservation area was better compared to those in non-conservation areas in terms of volume and stem density. The high variability observed in volume and biomass was attributed to forest types, accessibility, and altitude. Mean volume and biomass did not vary significantly in terms of slope classes and aspects. It is suggested that results obtained from the present study is useful as a baseline in analysing the changes in forest health, measured in terms of biomass and volume.