The type species, Sinusonasus magnodens, was named and described by Xu Xing and Wang Xiaolin in 2004. The generic name refers to the sinusoid form, in lateral view, of the nasals. The specific name means "big-toothed" in Latin. In a later publication the species is referred to as "Sinucerasaurus" but this is a junior objective synonym.
The holotype, IVPP V 11527, was found in the Lujiatun Member of the Yixian Formation, dating from the Hauterivian. It consists of a partial skeleton including skull and lower jaw fragments and partial tail, pelvis and hind limbs. The maxillary teeth are large. The femur is 141 millimetres long. The chevrons on the caudal vertebrae are so wide that they connect, forming a continuous plate at the underside of the tail.