To evaluate the responsiveness of power Doppler ultrasonography (PDUS) in comparison with conventional measures of disease activity and structural damage in rheumatoid arthritis (RA) patients receiving tocilizumab (TCZ). Seven RA patients with active arthritis were enrolled in the study and prospectively monitored for 12 months. They were treated with TCZ (8 mg/kg) every 4 weeks as monotherapy or in combination with disease-modifying antirheumatic drugs (DMARDs). Clinical, laboratory, and ultrasound examinations were conducted at baseline, 1, 3, 6, 9, and 12 months. Power Doppler (PD) signals were graded from 0 to 3 in 24 joints, and total PD score was calculated as the sum of scores of individual joints. One-year radiographic progression of the hands was estimated by using Genant-modified Sharp scoring. The averages of the clinical parameters rapidly improved, and all patients achieved good response within 6 months based on standard 28-joint Disease Activity Score (DAS28). Although the average total PD score declined in parallel with clinical improvement, radiography of the hands showed progression of destruction in the joints where PD signals remained, even among clinical responders. ΔSharp score correlated with the time-integrated value (TIV) of total PD scores (Δtotal Sharp score: r = 0.77, P = 0.04; Δerosion: r = 0.78, P = 0.04; Δjoint-space narrowing (JSN): r = 0.75, P = 0.05), but not with TIVs of clinical parameters including DAS28. PDUS can independently evaluate disease activity in RA patients receiving TCZ and is superior to DAS28, especially in predicting joint destruction.