In this paper, a hybrid algorithm by combining 15 task assignment rules and Ant Colony Optimization (ACO) algorithm to solve straight and U-type assembly line balancing problem to optimize line efficiency and smoothness index is proposed. The algorithm is designed to solve assembly line balancing problems of all sizes. The proposed multi-rule multiobjective ant colony optimization algorithm for straight and Utype assembly line balancing problems is evaluated with various set of benchmark problems and compared with a multi-objective simulated annealing algorithm reported in the literature. The results indicate the better performance of the proposed hybrid algorithm. © 2009 IEEE.