Purpose: Achilles tendonitis and plantar fasciitis are features of spondyloarthritis (SpA) that are used to evaluate the activity of SpA. There were few reports about the association between osteophytes at the entheses and the thickness of entheseal insertions. We aimed to clarify the association between osteophytes at the enthesis of calcaneus and the thickness of Achilles and plantar entheseal insertions. Subjects and Methods: We screened for SpA in 165 patients between June 2014 and November 2015. We excluded the patients who were diagnosed with SpA, rheumatoid arthritis, and other collagen diseases, and who had heel pain. Ninety-one feet were included. We evaluated osteophytes at the enthesis of calcaneus (lateral image) and the thickness of Achilles and plantar entheseal insertions by ultrasound examination. Results and Discussion: In the case of Achilles entheseal insertions, the thickness of positive osteophytes at the enthesis was thicker than that of non-osteophytes at the enthesis (4.45±0.78 and 3.96±0.65, p〈0.01). In the case of plantar entheseal insertions, there was no association between the thickness and osteophytes at the enthesis (2.85±0.48 and 2.77±0.64, p=0.52). Osteophytes at the enthesis of the Achilles tendon develop within the insertions, but osteophytes at the enthesis of the plantar fascia do not develop within the plantar fascia. This difference may reflect the mechanism of the osteophyte during enthesis formation. Conclusion: Osteophytes at the enthesis may cause thicker Achilles entheseal insertions. Therefore, we should carefully interpret the thickness of calcaneus insertions in cases with an osteophyte at the enthesis.