We report measurements of CP violation parameters in B{sup 0â}K{sup 0Ï0} decays based on a data sample of 657x10⁶BB pairs collected with the Belle detector at the KEKB e{sup +}e⁻ asymmetric-energy collider. We use B{sup 0â}K{sub S}{sup 0Ï0} decays for both mixing-induced and direct CP violating asymmetry measurements and B{sup 0â}K{sub L}{sup 0Ï0} decays for the direct CP violation measurement. The CP violation parameters obtained are sin2Ïâ{sup eff}=+0.67{+-}0.31(stat){+-}0.08(syst) and A{sub K}°{sub Ï}°=+0.14{+-}0.13(stat){+-}0.06(syst). The branching fraction of B{sup 0â}K{sup 0Ï0} decay is measured to be B(B{sup 0â}K{sup 0Ï0})=(8.7{+-}0.5(stat.){+-}0.6(syst.))x10⁻⁶. The observed A{sub K}°{sub Ï}° value differs by 1.9 standard deviations from the value expected from an isospin sum rule.