We have successfully developed a computer simulation technique for microstructural development such as sintering and grain growth of nano/micro-size particles. The molecular dynamic (MD) method, the Monte Carlo (MC) method and the finite element method (FEM) have been used for the simulations. The MD simulation, which was applied to alumina base ceramics, demonstrated the atomic structures and excess energy at grain boundaries and interfaces. The MC simulations were performed for the array of two- or three-dimensional lattices. Plural mechanisms of mass transport were introduced in the MC simulations of sintering and grain growth in ceramic systems, which involve a liquid phase and second solid particles. The combination method between MC and FEM has been developed to simulate precise shrinkage behaviors during sintering process.