OBJECTIVES: Extracorporeal shockwave therapy (ESWT) and corticosteroid injection (CSI) are treatment options for plantar fasciitis. Their clinical outcome comparison remains a debate. Also, the thickness changes of the plantar fascia on objective evaluation under the medium energy ESWT and CSI therapy are elusive. METHODS: A total of 97 patients with chronic plantar fasciitis were enrolled in the randomized prospective trial. Forty-seven patients received extracorporeal shock wave therapy (ESWT), and fifty patients received corticosteroid injection (CSI). The thickness of the plantar fascia was evaluated respectively before ESWT and CSI, and at the 4 and 12 week after ESWT and CSI by ultrasonography. Pain level and clinical outcomes were recorded using visual analogue scale (VAS) and 100-points scoring systems. Correlation analysis was performed between the thickness change and clinical outcome. RESULTS: Under ultrasonography, we observed more increase of plantar fascia thickness of ESWT group than CSI group at 4 week (p=0.048). VAS of plantar fasciitis patients receiving ESWT was lower than those who received corticosteroid injection (0.001 and p⟨0.001, at 4 and 12 week). On the assessment of 100-points scoring systems, the pain level of patients with ESWT was lower than those with CSI at the 12 week (p⟨0.001). On the other hand, the increase of plantar fascia thickness at 4 week was positively correlated with the decrease of VAS score at 12 week follow-up (R=0.302, P=0.039). CONCLUSIONS: At 4 week after treatment, the thickness of plantar fascia increased. Then it decreased gradually, but not to the baseline at 12 week. On the pain level outcome at 12 week, extracorporeal shockwave therapy (ESWT) was more efficient than corticosteroid injection (CSI) on chronic plantar fasciitis. The more change of plantar fascia after ESWT, the more efficient on clinical outcome.