An object-oriented (OO) model for three-phase unbalanced distribution system is proposed and implemented. Single-phase system components are initially modeled using object-oriented methodology. Later, it is extended to unbalanced three-phase distribution system using the "composition" technique of object-oriented design. The main features of object-oriented methodology such as "inheritance", "aggregation", "association" and "polymorphism" have been exploited to obtain a better software model. Three-phase distribution load flow analysis and short circuit analysis modules have been developed using the proposed object model. The performance of the developed software has been tested on IEEE 13-Node, IEEE 34-Node and IEEE 123-Node distribution systems. © 2006 Elsevier B.V. All rights reserved.