Highly cross-linked polyethylene (HXPE) in total hip arthroplasty has been shown to decrease wear rate compared with conventional liner. However, it has some disadvantages in that the mechanical properties cause early failure of the implant. This case report presents an unexpected failure of total hip arthroplasty in a 72-year-old woman that occurred at 20 months postsurgery. Operative findings revealed fracture of superior rim at locking groove of liner. We concluded that the failure was caused by decreased mechanical properties of highly cross-linked polyethylene, less thickness of polyethylene, more vertical cup, and use of large femoral head.