We analyzed the microstructure and degree of mineralization of the subchondral trabecular bone in hip osteoarthritis (OA) using synchrotron radiation computed tomography (SRCT) to identify the relationship between bone structure and bone turnover. Subchondral bone samples were extracted from femoral heads of 10 terminal-staged hip OA patients. The SRCT scan was performed at 30 keV energy and 5.9 µm voxel size. Trabecular bone structure, bone cyst volume, and the degree of trabecular bone mineralization were measured, and correlations between bone structure and the degree of mineralization were analyzed. In addition, the trabecular bone was divided into the area immediately surrounding the bone cyst and the remaining area, and they were compared. The average cyst volume fraction in the whole region was 31.8%, and the bone volume fraction in the bone region was 55.6%. Cyst volume was the only structural parameter that had a significant correlation with the degree of mineralization. The degree of mineralization was diminished when the bone cyst was larger (r = −0.81, p = 0.004). The trabecular bone immediately surrounding the bone cyst had a lower degree of mineralization when compared with the remaining trabecular bone (p = 0.008). In the bone sclerosis of OA subchondral bone, there are many large and small bone cysts, which are expected to play a significant part in the high bone turnover of OA. © 2012 American Society for Bone and Mineral Research.