The thesis examined lexical characteristics, word order, sentence patterns, and lexical meaning of Lao Song or Black Tai as well as compared words and their meanings in Lao Song with those in Thai. The data were collected from four language informants, two males, and two females, residing at Tambon Nong Song Hong, Ban Phaew District, Samut Sakhorn Province. The study findings revealed that, morphologically, there were monosyllabic and disyllabic words, which could be divided into compounding and reduplicating words. Syntactically, word orders were similar to those in Thai. Positive statements were used mostly, consisting of Subject + Verb + Object, as in “phor kamlang kin khao yuu” (father is eating). It can consist of only Subject + Verb, as in “morkhao duat” (the pot is boiling). Or the subject can be omitted, as in “hiw khao” (hungry rice = (I am) hungry). Or it can contain only a verb, as in “saphom” (shampooing). It all depends on questions asked and how to answer properly.