  We present a measurement of CP-violating asymmetries in B0 -> pi+pi- decays
based on 41.8 fb-1 data sample collected at the Y(4S) resonance with the Belle
detector at the KEKB asymmetric-energy e+e- collider. From the asymmetry in the
distribution of the time intervals between the two B meson decay points, we
obtain the CP-violating asymmetry parameters S_pipi = -1.21 + 0.38 - 0.27
(stat) + 0.16 - 0.13 (syst) and A_pipi = +0.94 + 0.25 - 0.31 (stat) +- 0.09
(syst).
