  We present a precise measurement of the standard model CP-violation parameter
sin(2phi1) based on a sample of 152 x 10^6 BB-bar pairs collected at the
Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy
e+e- collider. One neutral B meson is reconstructed in a J/psi Ks0, psi(2S)
Ks0, chi_c1 Ks0, eta_c Ks0, J/psi K*0, or J/psi KL CP-eigenstate decay channel
and the flavor of the accompanying B meson is identified from its decay
products. From the asymmetry in the distribution of the time interval between
the two B meson decay points, we obtain sin(2phi1) = 0.733 +/- 0.057(stat) +/-
0.028(syst).
