The time-dependent rate asymmetry of initial K 0 and K 0 decaying into π + π - π 0 was measured in order to reveal the CP-violating amplitude of the K S → π + π - π 0 decay. For the real and the imaginary parts of η + - 0 , we find Re(η + - 0 ) = (6 ± 13 s t a t . ± 1 s y s t . ) 10 - 3 and Im(η + - 0 ) = (-2 ± 18 s t a t . ± 3 s y s t . ) 10 - 3 which correspond to η + - 0 < 0.037 with 90% CL.