SOFL is a formal language and method for system specification and design. It was developed by integrating Petri Nets, Data Flow Diagrams, and VDM-SL. As the major feature of the original SOFL method is to use structured techniques for analysis and specification, and object-oriented techniques for design and implementation, SOFL has its own implementation language that is similar to C++. However, during our recent work of applying SOFL to software systems, the transformation of structured specifications to object-oriented implementations creates some difficulties, simply because of paradigms mismatch. In this paper we extend SOFL to a formal object-oriented language and method while keeping its structured features. This will allow powerful object-oriented reuse mechanisms, such as class inheritance and object compositio, to be utilized in the early phases, and transformation from SOFL specifications to commercial object-oriented programming languages to be readily achieved.