  We present the results of an age determination study for pre-main sequence
stars in the Ophiuchus molecular cloud. The ages of eight pre-main sequence
stars were estimated from surface gravities derived from high-resolution
spectroscopy. The average age of the target stars was 0.7 Myr. By comparing the
individual age and the near-infrared color excess, we found that color excess
decreases gradually with a constant rate and the lifetime of the inner disk was
determined to be 1.2 Myr. The estimated lifetime is nearly a half of the time
compared to that of the pre-main sequence stars in the Taurus molecular cloud
estimated with the same method. This result indicates that the disk evolution
timescale depends on the environment of the star-forming region.
