In this paper, we introduce a new assembly line balancing problem in which tasks differ with respectto their qualification requirements and the qualification levels of workers are ranked hierarchically. Inthe hierarchical workforce structure, a lower qualified worker can be substituted by higher qualifiedones with a higher cost. The resulting problem is referred to as assembly line balancing with hierarchicalworker assignment (ALBHW). The ALBHW problem consists in finding the optimal assignment of workersand tasks to the stations such that total cost is minimized. We have formulated an integer linear pro-gramming model to solve this problem. The computational results are obtained and analyzed on a largenumber of ALBHW instances.