In order to construct a well-characterized initial microstructure for Monte-Carlo simulation, computer-generated two dimensional modcl-microstructures were obtained by a mosaic method, and the characteristics of grains were analyzed. In this method, a microstructure is represented by a system consisting of 200• 200 lattice sites which are arranged periodically with a triangular shape. On this lattice, five microstructures, each consisting of 1000 grains with 100 randomly distributed orientations, were generated. The diameter and areal distribution of grains were in accordance with a gamma function, whereas the distribution of the number of sides shows a log-normal function, which was attributed to the behaviors of the grains of extreme shapes. Overall, the model-microstructure is suitable for the simulation of oriented grain growth since the topological characteristics, such as the relationships among the diameter, areal size and the number of sides of grains, are close to what are observed in real microstructures.