Abstract: In comparison with traditional software, the operational environment of Web services has been changed significantly. The operational environment of Web services is no long closed but open. The operational profiles under open environment are much more complex and unpredictable. It is an important property for the operational profiles under open environment to change continually over time. Because there are closed relationships between software reliability and operational profiles, this kind of varying operational profiles must affect the reliability. A natural hypothesis arises: the reliability of Web services is not only related to operational profiles, but should also be related to the change of operational profiles. As a first step, the authors studied this question by a case study. In this study, the derivative of operational profiles is used to indicate the change rate of operational profiles. Then based on the real Web services data, they did a number of statistics tests to test if the reliability of Web services is related to the change rate of operational profiles. In this paper, the contingency table analysis is used to do the independent tests. From the statistics tests, it comes to a conclusion that the reliability of the Web services depends on the changing rate of operational profiles significantly.