Teaching duty assignment is an important aspect of human resource management in a secondary school. This problem is currently solved by human planners. A prototype of an Intelligent Decision Support System for Teaching Duty Assignments (TDAS) has been successfully constructed and validated. The assignment aims to incur minimum dissatisfaction to teachers by distributing workload evenly among teachers. The automation of such a planning activity can reduce the pressure on a planner that are induced from the anxiety of teachers of being manipulated by the human planner. This system is the first of its kind in Hong Kong secondary schools. The algorithms have been tested on a set of real life data of a secondary school. The result was compared with its counterpart which was produced manually by the school principal with favourable comments that the computer result was usable.