Abstract: Often, because of inappropriate work design, an assembly is unbalanced. As a case problem, a study is conducted to balance an electric control board assembly line in a plant. After an investigation for the line, the line balancing problem is formulated as an optimization model. Then, by analyzing the model, the constraints in the model are transferred into a set of rules. Based on these rules, a heuristic is developed to solve the problem. Consequently, the line balancing is significantly improved and the productivity is increased.