Web services provide means to computerize e-business processes. To be able to satisfy business requirements web services must be developed rapidly and in high quality. Code generation techniques are frequently employed. In such context, verification of web service models emerges as a relevant issue: model verification makes it easier to detect and remove errors of system specification at the early stages of software development cycle. Available model verification tools require transformation of the objective model into complex formal notations, supported by the tool. It would be convenient to implement model verification directly in a CASE tool. This thesis describes a method for checking web service models based on verification of UML state machines. Conceptual algorithms for checking state machine’s safety criteria: reachability, completeness and consistency are provided. These algorithms, implemented in CASE tools could help to ensure the correctness and consistency of behavioral models. Also, a state machine template for composite web services is presented. Template complements state machine with transitions representing unsuccessful scenarios. Designer is freed from necessity to repeat reoccurring unsuccessful transitions for every event. This template is useful for automatic code generation.