Objective To explore the MRI features of juvenile-onset ankylosing spondylitis (JoAS) for improving the level of diagnosis and therapy. Methods MRI findings of JoAS in 25 patients confirmed by clinical and laboratory results between October 2010 and September 2014 were retrospectively analyzed. Results There were a total of 67 locations of lesion in the 25 cases, including 19 in sacroiliac joint, 21 in hip joint, 6 in ischial tuberosity, 6 in crista iliaca, 9 in knee joint, 4 in ankle joint, and 2 in foot. MRI showed 63 locations with bone marrow edema, 36 with joint effusion, 26 with bone destruction, and 19 with enthesitis. Conclusions Bone marrow edema is the most common MRI manifestation of JoAS, and the main bone destruction is middle axis joint. MRI is sensitive but not specific to lesions, so differential diagnosis is needed and helpful.