Abstract: The four existing Functional Size Mcasurement(FSM) methods that meet the ISO standards can not take the interactions and behaviors of objects into consideration and can not correctly measure the functional size of object oriented systems. So, based on the analysis of software development process of object oriented methods, according to the characteristic of object-oriented systems,this paper presented an Object Oriented Full Function Point method based on COSMIG-FFP, and gave the mapping rules, measurement rules and an example of the application process of the approach. I}his method provided an effective way for the correct measure of the function size of object oriented systems.

Key words: Object-oriented method, Functional size measure(FSM)，COSMIC-FFP, Object-oriented full function point(OOFFP)，Mapping