Rift Valley fever virus is a zoonotic pathogen that is transmitted between mosquitoes and mammals such as sheep, cattle and humans. It is an enveloped negative-sense single-stranded RNA virus, which is a member of the family Bunyaviridae and the genus Phlebovirus. During replication, RVFV produces a 78 kDa glycoprotein NSm1 of unknown function, believed to be nonstructural. Here I show that NSm1 is incorporated into RVFV virions assembled in C6/36 mosquito cells, but not in virions assembled in Vero E6 mammalian cells. The presence of NSm1 in insect-amplified virions was demonstrated through repeated immunoblots of purified virions and further supported by mass spectrophotometric confirmation of the identity of immunoblot-positive protein bands. This research appears to be the first evidence that distinct viral protein profiles are correlated to the host cell in which replication occurred.