Radio Frequency IDentification (RFID) is a radio communication technique. It identifies specific targets and acquires related data from the backend database by using radio frequency signal and no physical touch needed. Because of its advantages of low cost and remote identity-recognition, this technology has been widely used in many applications. However, the information, which is transmitted via radio signal, is easily eavesdropped and traced by an attacker. Therefore, it is important to design a secure RFID protocol which can ensure the authentication of the origin and the integrity of the transmitted information. Researchers have put their efforts into this field and proposed many solutions to deal with these issues. In particular, in 2012, Bassil et al. introduced an ultra-lightweight RFID protocol based on a physical unclonable function (PUF), which means that the tags in the RFID architecture are unclonable. However, the insecurity of the scheme has been pointed out recently. In this paper, we will propose a new ultra-lightweight RFID protocol based on PUF that can overcome the security loopholes occurs in Bassil et al.'s protocol.