In the present study, we tested the memory performance of different mouse strains (129/Sv, BALB/c, C57BL and Swiss) in an object recognition task. In this one-trial learning task, mice showed a good object memory performance when a 1-h delay was interposed between the first and second trial. However, when a 24-h delay was used, the mice did not discriminate between the novel and the familiar object in the second trial, indicating that the mice did not remember the object, which was presented in the first trial. Using a 4-h delay, the discrimination performance was at an intermediate level, suggesting a delay-dependent forgetting in this task. Although strain differences were found in the absolute level of exploration activity, no strain differences were found on the relative discrimination index (d2). The present data show that object memory can be assessed in mice and, in contrast to other memory tasks, appears to be less strain-dependent. The reliability of the discrimination measures is discussed.