ABSTRACT Objectives Intra-articular corticosteroid injection (IACI) is a safe first-line or adjunct therapy used in any subtype of juvenile idiopathic arthritis (JIA). Limited studies evaluated the effect of IACI on cartilage. Our study aimed to examine the femoral cartilage thickness of patients with JIA who received IACI to the knee joint using ultrasound. Methods We randomly selected JIA patients who performed IACI in the knee joint. Baseline bilateral joint cartilage and tendon thicknesses were measured. The articular fluid was aspirated, and applied IACI at the same period. Six months after injection, the exact measurements were repeated. Distal femoral cartilage, quadriceps tendon, and distal and proximal patellar tendon thicknesses were compared at the baseline (before IACI) and 6 months after IACI. Results Thirty patients with JIA were included, and 23 (76.7%) were female. The median age was 11 years (interquartile range, 6 to 14), and the median disease duration was 3.3 years (interquartile range, 5 months to 5 years). The subtypes of JIA were oligoarticular in 25 (83.3%), polyarticular in 2 (6.7%), enthesitis-related arthritis in 2 (6.7%), and juvenile psoriatic arthritis in 1 (3.3%). Distal femoral cartilage thickness was 2.96 ± 0.79 mm at baseline and 2.85 ± 0.70 mm at 6 months after IACI (P = .35). The tendon thicknesses were similar at 6 months after baseline measurements. Conclusions Our findings reveal that knee IACI in patients with JIA did not significantly change cartilage and tendon thicknesses. This observation could indicate that IACIs have no detrimental effects on the cartilage and the tendons.