A print head assembly and a printer using the same are disclosed. The print head assembly includes: a bracket, a print head and an elastic element. The bracket includes a first bracket body having a cavity and a lid covered on the opening of the cavity. A window is opened on the first bracket body. The print head is accommodated in the cavity of the first bracket body and hinged to the first bracket body via a first rotary shaft. The surface of a heating element of the print head is matched with the window and faces an outside paper pressing roller. The elastic element biases towards the print head so as to make the surface of the heating element of the print head have a tendency to extend outside the window. The print head assembly is capable of being detached as a whole, thus the requirements of performing single-sided printing and duplex printing in the same printer is achieved.