The quadratic assignment problems (QAPs) are the problem of assigning 'n' facilities to 'n' locations so that the assignment cost is minimized, where the cost is defined by a quadratic function. In this paper we investigate and present the application of population based hybrid ant-colony system (PHAS) metaheuristic for solving machine (facility) layout problems formulated as quadratic assignment problem, a well-known NP hard combinatorial optimization problem. Ant-colony system is a model for designing metaheuristic algorithms for combinatorial optimization problems. The PHAS ant system algorithm incorporates population-based ants in its initial phase instead of small number of ants and probability based pheromone trail modification. We tested our algorithm on the benchmark instances of QAPLIB, a well-known library of QAP instances and the obtained solution quality is compared with solution obtained with standard guided local search algorithm for the same QAP. © 2006 IEEE.