The conduction-electron diamagnetism has been calculated for the three-dimensional band structure of graphite. The magnetic energy levels are found and the susceptibility calculated by analytically carrying out the free energy sum. Agreement with experiment is found for values of the band parameters nearly equal to those which give agreement with the de Haas-van Alphen effect and other phenomena. The value of γ0 is found to be 2.8+/-0.1 ev. The results indicate the γ1 is about 0.27 ev and ∆ is about 0.025. The other band parameters do not have an important influence upon the value of the susceptibility. The relation to the general treatments of conduction-electron diamagnetism is also discussed.