We measure the time-dependent CP violation parameters in B0→KS0KS0KS0 decays using 772×106BB¯ pairs collected at the ϒ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider. The obtained mixing-induced and direct CP asymmetries are -0.71±0.23 (stat)±0.05 (syst) and 0.12±0.16 (stat)±0.05 (syst), respectively. These values are consistent with the Standard Model predictions. The significance of CP violation differs from zero by 2.5 standard deviations. © 2021 authors. Published by the American Physical Society.