A circuit and a method for measuring rising or falling time of high-speed data are disclosed. The circuit includes a comparator and a storage circuit. The comparator receives the high-speed data via a first port and a reference signal via a second port, compares a level of the high-speed data with a level of the reference signal in response to an enable signal, and outputs the compared result as a signal. A reference signal generator generates the reference signal. An enable signal generator generates the enable signal. The storage circuit receives and stores the signal and measures the rising or falling time of the high-speed data.