Abstract Background Rotational atherectomy (RA) has improved percutaneous treatment of severe coronary calcified lesions, but the "no-reflow" phenomenon remains a serious complication. Platelet activation by RA may contribute to the no-reflow, we use OCT to test the effect of RA on platelet aggregation. Methods We analyzed 20 consecutive patients with severe coronary calcified lesions by OCT imaging performed before and after RA and after stent implantation. Results Mean burr size was 1.48 ± 0.14. Mean rotation speed was 152,300 ± 4,200 rpm. Mean number of rotations per patient was 5.3 ± 2.1 times and mean ablation time per RA was 11.3 ± 3.2 seconds. All the target vessels had platelet aggregation on OCT after RA. The average number of white thrombus per lesion after RA was 7.23 ± 4.4, and the average length of every white thrombus was 0.51 ± 0.33 mm. In Pearson Correlation Analysis, platelet aggregation load was related with burr size (r = 0.575, P = 0.040) and rotation number (r = 0.599, P = 0.031). Conclusions Platelet aggregation during RA is proved by OCT in vivo. The bigger burr size, higher number of ablation times, maybe together with higher rotation speed can influence the platelet aggregation load. These data suggest a proper RA strategy to avoid no-reflow during RA.