The heat capacity of Nb3Sn has been measured between 16.0°K and 20.3°K. A jump in specific heat at Tc is found with ΔC = 2.21 (±5%) joule/mole·deg. The transition temperature of the sample is Tc= 17.88°K, and the transition interval is ΔTc ≈ 0.2°K. From the measured ΔC and by using the thermodynamic relationship, the thermodynamic critical magnetic field at 0°K, H0≈5300 Oe, was obtained. Using the result of ΔC obtained in the present work, and the jump of the thermo-expansion coefficient Δα and (?Tc/(?p) from the literatures, the thermodynamic relation be-tween these quantities was found to be valid.Apparatus for measuring the specific heat is briefly described.