Resource allocation in computational grids is considered as a NP-Complete problem due to resources heterogeneity. Grid resources are related to various management areas exerting different management policies. Nowadays, enhancing grid efficiency is regarded as a problem requiring proper and effective schedule. Unfortunately, grid resources dynamic nature, in addition to the variety of users’ requests has intensified grid resource allocation. The present paper offers a new heuristic method based on Particle Swarm Optimization (PSO) algorithm for resource allocation in grid environment. The proposed method creates an optimal scheduling in task completion with minimum flowtime and makespane.