In 1988, a Chinese-Canadian expedition discovered the remains of a small theropod near Huamuxiao, in the Ordos Basin of Inner Mongolia.

Sinornithoides youngi, the type species, was named and described in 1993/1994 by Dale Russell and Dong Zhiming based on this fossil specimen from the Lower Cretaceous Ejinhoro Formation.

The generic name is derived from Latin Sinae, "Chinese", and Greek ὄρνις, ornis, "bird", en ~ειδής, ~eides, a suffix meaning "~like", in reference to the bird-like build.

The holotype is preserved in much the same roosting position as another troodontid fossil, that of Mei long, with its snout tucked under its left hand.

Troodontids have sickle-claws and raptorial hands, and some of the highest non-avian encephalization quotients, meaning they were behaviourally advanced and had keen senses.

[5] In 1994, Sinornithoides was one of the most completely known troodontids, especially as regarded the palate, but the lack of sufficient fossil material to compare it with induced Russell and Dong not to indicate any diagnostic traits.

[2] A possible position of Sinornithoides in the evolutionary tree of the Paraves is shown by the cladogram below, following a 2012 analysis by Turner, Makovicky and Norell.