Moisture absorption into hygroscopic/hydrophilic materials used in fused deposition modeling (FDM) and ultrasonic welding (USW) can diminish desired mechanical properties. Sensitivity to moisture is dependent on material properties and environmental factors and needs characterization. In this thesis, moisture sensitivity of PLA filaments and PLA/PBS blended filaments was characterized in FDM printed ASTM test samples post-conditioning the filaments at different relative humidity levels. Tensile strength decreased with increase in moisture content. Parts made with PLA 4043D, PLA/PBS 75/25 filaments were most sensitive to moisture. Investigation of tensile properties of parts made with PLA filaments exposed to room temperature and humidity conditions for three months showed a more significant decrease. Moisture sensitivity of PLA, PBS, and PLA/PBS 25/75 blend characterized for USW using injection-molded industrial standard test parts (ISTeP) showed a downward trend in weld strength for 100% PLA and PLA/PBS 25/75 while 100% PBS was significantly affected at high moisture conditions.