With the popularity of PC and the coming of Internet era, more and more software systems are constructed under a distributed object-oriented environment. Software systems constructed with the distributed object-oriented technology have the advantages of openness, modularization, flexibility and easy maintenance. Also, a distributed software system can efficiently solve the problems that need complicated computing. However, testing and debugging in the later stage of software development demand great deal of resources, and open-environment architecture of general distributed systems tends to increase the complexity of testing. To resolve the problems mentioned above, this work proposed a Generic Tester for distributed object-oriented systems. This Generic Tester is applicable to the tests of an individual component or module and even the whole distributed object-oriented system as long as the functions and operations of the components or system can be presented with only class diagrams (as well as interface definitions) and sequence diagrams generated by the tools used during software development. Research results indicate that this Generic Tester enables an integrated planning of software development and testing, reduces testing cost, and improves overall development efficiency.