  X-ray properties of the BL Lacertae object OJ 287, observed with ASCA on 1997
April 26 and November 17, are reported. The 0.5 -- 10 keV flux was lower than
those obtained in previous X-ray observations, and no evidence of intensity
variations was found during each observation. The obtained flux densities at 1
keV, 0.22~0.26 uJy, exceed the extrapolations from lower frequency synchrotron
continua, which were measured in nearly the same period as the present ASCA
observations. The X-ray spectra acquired with the GIS and SIS were consistently
described with a single power law model modified with the Galactic absorption,
and the derived photon indices, 1.5 ~ 1.6, are flatter than those observed so
far. These results strongly suggest that the X-ray spectra observed in 1997
arise via inverse Compton process alone. The X-ray spectra obtained in 1994
(Idesawa et al 1997), exhibiting a steeper slope than those in 1997, is thought
to be contaminated by "synchrotron soft tail".
