<p>The problem of crystallization of a molten particle with an initial temperature equal to the melting point is investigated during convective heat exchange on the surface. The heat conduction equation is solved for a region with movable interphase boundaries, the law of movement of which is not known in advance. For small-sized particles, analytical expressions are obtained that describe the propagation of the crystallization front, and the crystallization time with indication of applicability limits.</p>