TITLE: GCN CIRCULAR NUMBER: 31737 SUBJECT: GRB 220306B: Nanshan/NEXT optical upper limit DATE: 22/03/11 09:14:31 GMT FROM: Dong Xu at NAOC/CAS S.Y. Fu, X. Liu, S.Q. Jiang, D. Xu (NAOC), Z.P. Zhu (NAOC, HUST), X. Gao (Urumqi No.1 Senior High School), J.Z. Liu (XAO) report: We observed the field of Swift GRB 220306B (Caputo et al., GCN 31697) using the NEXT-0.6m telescope located at Nanshan, Xinjiang, China. We obtained 3x40 s and 1x60 s frames in the Sloan r-band, starting at 18:23:35 UT on 2022-03-06, i.e., 478 s after the BAT trigger. No optical source is detected at the Enhanced Swift/XRT position (Evans et al., GCN 31700) in our stacked image, down to a limiting magnitude of r~19.3, calibrated with the nearby PanSTARRS field.