The theoretical basis of Ostwald ripening has been reviewed with particular reference to the effect of medium grain fraction on the size distribution. And the procedure to obtain a reliable size distribution by linear intercept method has been specified in detail for cobalt grains in 50% Co-50% Cu alloy at 1,200℃. Systematic tests are performed to confirm the validity of the observed grain intercept distributions. The shortcomings of chi-square test are discussed. The grain intercept distribution approaches to a stabilized form when the number of intercepts reaches about 1,000 and that of photo-micrographs 5 to 6. This result does not vary with the grouping method of intercept size classes. During coarsening, the size distribution maintains a stationary form, which is consistent with the theoretical predictions for diffusion controlled growth when the grain volume fraction exceeds about 0.5.