To measure the professional identity of teachers one needs to construct an instrument that is valid and reliable. To this end, based on the theoretical definition of professional identity, its constituents were initially derived, based on which a 34-item questionnaire was constructed. The validity of the instrument was confirmed by the experts, while its internal consistency was measured to be 0.94. To collect data a cluster sample of 217 elementary school teachers from among all 501 such teachers in the city of Yasuj was selected. Factor analyses of the collected data lead to identification of 8 constituents and removal of 4 of the items. The identified constituents are as follow: professional, socio-cultural, artistic, field related, economic, attitudinal, personal, and political.