Operability study is a systematic technique for identifying hazards or operability problems throughout an entire facility, but requires a labor-intensive and time-consuming process. This paper presents an algorithm for a computer-aided operability study for batch plantg using knowledge engineering. The batch plant Operation consists of these three processes ＇＇charge,＇＇ ＇＇reaction＇＇ and ＇＇discharge.＇＇ Operability study for batch plants should be carried out for each operating step. The knowledge to perform the operability study is separated into plant specific knowledge and generic data to facilitate the development of widely applicable systems. Causal relationships between input variable deviations and output variable deviations for components of batch plants are modeled using decision tables and stored in the generic data base. The plant structure (Piping and Instrumentation Diagram) and reaction types are inputted to the plant specific knowledge base. Each process variable of equipment (manipulating variables, initial conditions of state variables and operating time) is examined in sequence by searching the generic data base, using key words to describe deviations. A computer-aided operability study is demonstrated for a polyvinyl acetate plant using the proposed methodology.