A memory device is provided, including a built-in self-test circuit and a redundancy address replacement circuit. The built-in self-test circuit coupled to a main memory cell array is configured to performing a built-in self-test process on the main memory cell array so as to provide a built-in self-test signal. The redundancy address replacement circuit includes a first redundancy circuit and a second redundancy circuit. The first redundancy circuit replaces portion of word line addresses of the main memory cell array with that of a redundancy memory block according to first redundancy data signals generated by a first test process. The second redundancy circuit, coupled to the first redundancy circuit, replaces the failure word line addresses detected in the main memory cell array with another portion of word line addresses of the redundancy memory block according to the built-in self-test signal.