Abstract: An Expert System for RC buildings aseismic disign (RCBAD) on microcomputer in accordance with TJ11-78 along with expertise about earthquake resistance is presented. RCBAD was developed using Smalltalk/V based On Object-Oriented Programming (OOP) technology. The expert system can be used to carry out preliminary aseismic design both multi-storied and high-rise RC buildings, as well as to calculate dynamic responses to check the earthquake performance by external Fortran program. The knowledge base in RCBAD is represented as hierarchical module according to the hierarchy and inhereitance, while the knowledge is incorporated in rules. This is a basis of expert system for structural design for it can be attached with other necessary functional modules as required.