We have searched for a time-modulated decay in a standard electron capture experiment for (140)pr in order to confirm a report from GSI, where an oscillatory decay has been observed for hydrogen-like Pr-140 and Pm-142 ions in the cooler storage ring. Pr-140 has been produced with the Ce-140(p, n) reaction by a pulsed proton beam accelerated from the Van de Graaff accelerator at Osaka University. Resultant time dependence of the k(alpha) and K-beta X-ray intensities from the daughter shows no oscillatory behavior.