  We observed a 17$'\times17'$ region of the $\rho$ Oph molecular cloud, using
the ACIS-I array onboard the {\it Chandra X-ray Observatory} (CXO). A 100-ks
exposure observation revealed $\sim$ hundred X-ray sources above the detection
limit of $\sim$ 10$^{28}$ ergs s$^{-1}$. About 2/3 of the X-ray sources are
identified to an optical and/or infrared counterpart, including significant
numbers of class I, II and III sources and a few brown dwarfs. The X-ray
detection rate of class I sources is surprisingly high of 70 %. Many X-ray
flares, possibly due to the magnetic activity, are found from all of the
classes. We make systematic spectral studies on the quiescent and flare X-rays
for all the X-ray sources. The X-ray temperatures and absorptions of class I
sources are generally larger than those of class II and III sources. Also X-ray
flares from class I sources show a hint of higher duty ratio, temperature and
luminosity, than those from more evolved classes. We further give brief results
on brown dwarfs, younger phase than class I, unclassified and unidentified
sources. Details for several selected young stellar objects, including the
first detection of a neutral iron line (6.4 keV) from a class I source YLW 16A,
are separately addressed.
