Purpose: Pregnancy is characterized by many musculoskeletal changes that affect daily living activities and walking. The purpose of this study was to examine the effect of pregnancy on pelvic and trunk kinematics, and their relationship during the three pregnancy trimesters. Methods: Three-dimensional pelvis and trunk motions were measured using Qualisys Gait Analysis System in the first, second and third trimesters of pregnancy. The maximum anterior pelvic tilt and maximum trunk flexion during stance phase, pelvic tilt, obliquity and rotation, as well as trunk flexion-extension, lateral bending and rotation were measured. Results: Repeated-measures analysis of variance showed a significant increase in the maximum anterior pelvic tilt during stance phase (p=0.005), and a significant decrease in the pelvic obliquity (p=0.011), maximum trunk flexion during stance phase (p=0.0006), trunk lateral bending (p=0.005) and trunk rotation (p=0.004). A significant negative correlation was found between maximum anterior pelvic tilt and maximum trunk flexion in the first (r=-0.72, p=0.008), second (r=-0.61, p=0.03), and third (r=-0.61,p=0.03) trimesters of pregnancy. Also, there was a significant positive correlation found between pelvic obliquity and trunk lateral bending in the first (r=0.76, p=0.04), second (r=0.59, p=0.04), and third (r=0.59, p=0.04) trimesters of pregnancy. Conclusions: The pregnant women walk with an increased maximum anterior pelvic tilt, a decreased maximum trunk flexion, a decreased pelvic obliquity, as well as a decreased trunk lateral bending and rotation. Pregnancy does not affect the relationship between pelvis and trunk motions.