An adjustable wheel cover for aluminum alloy rims is revealed. A wheel cover is disposed with through holes corresponding to hollow holes of an aluminum alloy rim. A peripheral wall is extended axially from an inner surface of the wheel cover and along a periphery of each through hole. At least one assembly part is formed on the peripheral wall and an insertion slot for receiving a fixing part is arranged at the assembly part axially. The assembly part is disposed with a plurality of adjustment holes radially. A locking block on a spring of the fixing part is secured in the adjustment hole correspondingly. Thus the wheel cover can be adjusted flexibly to fit the aluminum alloy rims with production tolerances. The problem of unstable connection between the wheel cover and the aluminum alloy rim caused by unmatched size can also be solved.