© 2014, The Author(s). Abstract: We present a measurement of the time-dependent CP violation parameters in B<sup>0</sup> → η′K<sup>0</sup> decays. The measurement is based on the full data sample containing 772 × 10<sup>6</sup> (Formula Presented.) pairs collected at the Υ(4S) resonance using the Belle detector at the KEKB asymmetric-energy e<sup>+</sup>e<sup>−</sup> collider. The measured values of the mixing-induced and direct CP violation parameters are: (Formula Presented.) (Formula Presented.) where the first uncertainty is statistical and the second is systematic. The values obtained are the most accurate to date. Furthermore, these results are consistent with our previous measurements and with the world-average value of sin 2ϕ<inf>1</inf> measured in B<sup>0</sup> → J/ψK<sup>0</sup> decays.