We report a measurement of decay-time-dependent charge-parity (CP) asymmetries in B0→KS0KS0KS0 decays. We use 387×106 BB ̄ pairs collected at the Υ(4S) resonance with the Belle II detector at the SuperKEKB asymmetric-energy electron-positron collider. We reconstruct 220 signal events and extract the CP-violating parameters S and C from a fit to the distribution of the decay-time difference between the two B mesons. The resulting confidence region is consistent with previous measurements in B0→KS0KS0KS0 and B0→(cc ̄)K0 decays and with predictions based on the standard model.
