The effect of image force on field emission of electrons from negatively charged solid particles has been analytically investigated and some numerical results have been presented in the form of a graph between ln (nem/F2) and 1/F, where nem is the emission rate per unit area and F is the surface field strength. The results have been compared with those obtained for a corresponding plane surface using the WKB approximation. It is seen that the variation for a spherical surface has a significant departure from the corresponding approximate straight line for a plane surface.