In this study, the effects of heat treatment on modulus of rupture (MOR), modulus of elasticity (MOE) and weight loss (WL) of beech (Fagus orientalis Lipsky.) and spruce (Picea orientalis (L.) Link.) woods were examined, and relationship between WL and the mechanical properties of the treated woods were determined by various analyzes. The experimental samples were selected from naturally grown woods in the Black Sea region of Turkey. Heat treatment was subjected to samples in an oven at three different temperatures (130, 160 and 190 degrees C) and three different durations (2, 6 and 10 h) under atmospheric pressure. The results indicated that treated samples had lower MOR and MOE compared to control samples. An increase in exposure temperature and duration decreased MOR and MOE. WL of the samples increased with increasing treatment temperature and duration. Also, percentage reduction in MOR and MOE values showed a strong correlation with percentage increase in WL. The correlation coefficient (R) was determined as 0.89 between MOR and WL, and almost 0.90 between MOE and WL.