Existing data of thermal variations of bulk coercivity Hc for various magnetic samples are shown to be linearly proportional to λ/Ms in the temperature range from the Verwey transition to the Neel temperature of magnetite, where λ is some appropriate magnetostriction constant and Ms is the saturation magnetization. This clearly indicates that the temperature stability of bulk coercivity in these magnetic samples is stress controlled, as concluded early by Hodych (1982, 1986) based on Hc data measured at low temperatures. However, no existing theories of bulk coercivity for multidomain grains are satisfactory at explaining this seemly simple λ/Ms dependency of Hc. Although other complexities may exist, we suggest a mechanism in which internal stress associated with dislocations in these samples not only causes domain wall pinning but also determines the anisotropy of domain walls. The theory thus developed is consistent with the observed temperature dependency of Hc. We further suggest that the temperature dependency of bulk coercivity of all magnetite grains is predominantly controlled by stress associated with dislocations, with a few exceptions such as for single-domain (or nearly single-domain) grains for which the stability is primarily controlled by grain shape. ¿ American Geophysical Union