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We interpret the observed radial-velocity curve of the optical star in thelow-mass X-ray binary 2S 0921-630 using a Roche model, taking into account theX-ray heating of the optical star and screening of X-rays coming from therelativistic object by the accretion disk. Consequences of possible anisotropyof the X-ray radiation are considered.We obtain relations between the masses ofthe optical and compact (X-ray) components, mv and mx, for orbital inclinationsi=60, 75, 90 degrees. Including X-ray heating enabled us to reduce the compactobject's mass by near 0.5-1Msun, compared to the case with no heating. Based onthe K0III spectral type of the optical component (with a probable mass ofmv=2.9Msun, we concluded that mx=2.45-2.55Msun (for i=75-90 degrees). If theK0III star has lost a substantial part of its mass as a result of massexchange, as in the V404 Cyg and GRS 1905+105 systems, and its mass is$m_v=0.65-0.75Msun, the compact object's mass is close to the standard mass ofa neutron star, mx=1.4Msun (for i=75-90 degrees). Thus, it is probable that theX-ray source in the 2S 0921-630 binary is an accreting neutron star.

The Mass of the Compact Object in the Low-Mass X-ray Binary 2S 0921-630