  The results of Multiple Mirror Telescope spectrophotometry of the extremely
low-metallicity blue compact galaxy (BCG) SBS 0335-052 are presented. The
oxygen abundance in central brightest part of the galaxy is found to be 12 +
log(O/H) = 7.33+-0.01. The N/O, Ne/O, S/O and Ar/O abundance ratios are close
to those derived in other BCGs, suggesting that heavy element enrichment in the
HII region is due to massive star evolution. We detect auroral [OIII] 4363
emission in the inner part of HII region with a diameter of 3.6 kpc and find
that the HII region inside this diameter is hot, T_e~20000K. The oxygen
abundance in this region is nearly constant (12 + log(O/H) = 7.1 - 7.3),
implying effective mixing of ionized gas on short time-scales. We also discuss
the origin of blue underlying extended low-intensity emission detected in SBS
0335-052. The (V-I) and (R-I) color distributions suggest that a significant
contribution to the extended envelope is due to ionized gas emission. However,
the observed equivalent width of Hbeta emission in the extended envelope is 2-3
times lower than the value expected in the case of pure gaseous emission. These
findings suggest that, along with the blue young (~10^7yr) stellar clusters, an
older stellar population with age ~10^8yr may be present in the extended
envelope of SBS 0335-052, having a total mass conclude that SBS 0335-052 is a
young nearby dwarf galaxy with age ~10^8 yr.
