  The middle-aged supernova remnant (SNR) N49B in the Large Magellanic Cloud
has been observed with the {\it Chandra X-Ray Observatory}. The superb angular
resolution of {\it Chandra} resolves the complex structure of X-ray emitting
filaments across the SNR. All observed features are soft ($E <$ 3 keV) and we
find no evidence for either point-like or extended hard emission within the
SNR. Spectral lines from O, Ne, Mg, Si, S, and Fe are present. Equivalent width
images for the detected elemental species and spatially-resolved spectral
analysis reveal the presence of Mg-rich ejecta within the SNR. We find no such
enrichment in O or Ne, which may reflect details of the nucleosynthesis process
or the heating and cooling of the ejecta as it evolved. The bright
circumferential filaments are emission from the shocked dense interstellar
medium (ISM). We detect faint diffuse X-ray emission that extends beyond the
X-ray bright filaments toward the west and southeast. These features appear to
be the blast wave shock front expanding into lower density portions of the ISM
seen in projection. We set an upper limit of $\sim$$2\times 10^{33}$ ergs
s$^{-1}$ on the 0.5 $-$ 5 keV band X-ray luminosity of any embedded compact
object.
