Microwave (MW) pretreatment was used to increase the impregnability of Oriental spruce sapwood (Picea orientalis (L.) Link.). Wood samples with moisture contents of 55% and 83% were subjected to different MW energy treatments (1156 MJ/m3 and 1542 MJ/m3). Additionally, the mechanical properties of the treated wood samples were tested to determine the degradation caused by exposure to the MW radiation. According to the test results, the average preservative material retention rates increased by 47.5% and 70% for the samples with initial moisture contents of 55% and 83%, respectively, compared to the reference samples. The mechanical properties of the MW pretreated wood samples decreased within the range of 1.7% to 2.9% in the case of the compression strength; changed within the range of (+)1.9% to (-)6.1% in case of the bending strength; and changed within the range of (+)0.9% to (-)6.2% in case of the modulus of elasticity (MOE). The application of MW energy at different power settings on the samples with similar moisture levels was determined to have no impact on the mechanical properties of treated wood.