The decay B 0 ->J/ψK 0 S is reconstructed with J/ψ->e + e - or μ + μ - and K 0 S ->π + π - . From the full ALEPH dataset at LEP1 of about 4 million hadronic Z decays, 23<space>candidates are selected with an estimated purity of 71%. They are used to measure the CP asymmetry of this decay, given by sin2β in the Standard Model, with the result sin2β=0.84 + 0 . 8 2 - 1 . 0 4 +/-0.16. This is combined with existing measurements from other experiments, and increases the confidence level that CP violation has been observed in this channel to 98%.