A pulse-echo acoustic method was investigated for evaluating wood stake decomposition in the field. A total of 58 wood stakes (29 loblolly pine, Pinus taeda, and 29 aspen, Populus tremuloides) that were vertically installed (full length) in forest soils were non-destructively tested by means of a laboratory-type acoustic measurement system. The same acoustic measurements were also conducted on the wood stakes after they were removed from the soil. Compression (parallel to grain) tests were then performed on the stakes in the laboratory to obtain residual elastic and strength properties. The results indicate that the pulse-echo acoustic method is a good approach to characterize wood stakes that are fully inserted into mineral soils. Statistical analysis showed good relationships between acoustic parameters (number of pulse echoes and in-ground acoustic velocity) and percentage weight loss, modulus of elasticity in compression, and residual compressive strength. The pulse-echo acoustic method could be used as a monitoring tool to assess progressive levels of wood stake decomposition in forest soil.