  A precise measurement of the direct CP violating charge asymmetry parameter
$A_g$ in $K^\pm\to\pi^\pm\pi^+\pi^-$ decays by the NA48/2 experiment at CERN
SPS is presented. The experiment has been designed not to be limited by
systematic uncertainties in the asymmetry measurement. A preliminary result for
the charge asymmetry $A_g=(-1.3\pm2.3)\times 10^{-4}$ has been obtained with a
sample of $3.11\times 10^9$ selected events corresponding to the full collected
statistics. The precision of the result is limited by the statistics used.
