This study investigates the levels of social language and vocabulary characteristics of three- to six-year-old children with autism in Vietnam. The research is based on analysis of the developmental assessment reports of 151 children with autism, and 42 parents' reports on their children's vocabulary (recorded using the Child Word Inventory form). The findings show that about 85% of participants have a language level that is below average. The rate of accumulation of words and social language by children with autism is slower than that of typically developing children of the same age. It is also found that the participants' number of production words is 2.4 times greater than their number of reception words. Nonetheless, their receptive words have little correlation with their overall development and social language development. This implies that parents and teachers of children with autism should make a point of assisting them in enlarging and comprehending their vocabulary, to enable them to use their language (words) for effective communication.