Аннотация:MASTER-IAC robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Spain (IAC Teide Observatory) started inspect of the Fermi GRB 210420A ( Fermi GBM team, GCN 29837) errorbox 76671 sec after notice time and 76698 sec after trigger time at 2021-04-21 02:27:47 UT, with upper limit up to 18.0 mag. The observations began at zenith distance = 19 deg. The sun altitude is -45.1 deg. The galactic latitude b = 31 deg., longitude l = 31 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=1596846 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________| _____________________|__________ ___________|_____________________ _______________|_____|_______|___ ____|________ 76728 | 2021-04-21 02:27:47 | MASTER- IAC | (16h 48m 60.00s , +28d 09m 03.3s) | C | 60 | 18.0 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited.