This research is a study of Hakka grammar, one of seven Chinese language groups, in the Sino-Tibetan family. Most people in Thailand know Hakka as bciin khaeʔc and language usage is declining now because there are only a few Hakka speakers and most of them are over 50-60 years old. The objective of this research is to describe Hakka grammar including morphemes, words, phrases, clauses, and sentences. The data was gathered between 2010- 2012 and rechecked from informants who live in Bangkok, who use the Meixian dialect. The tagmimic model (David Thomas, 1993) was used to analyze the linguistic data. Colloquial language was collected together with Chinese characters based on the main informant; there is no standard writing system because there is no Hakka written form. The researcher also compared differences between colloquial and reading pronunciations including a summary of how to select Chinese characters for colloquial pronunciation in Hakka. The results of the grammar found that the word order in Hakka is subject- verb- object (S-V-O). Word types can be divided into compounding, affixation, reduplication, and onomatopoeia. Prefixes were less common than suffixes and infix was not found in Hakka. The phrase level, phrases can be divided into major types. At the cluase level, cluases are divided into independent clauses or main clauses which function as main clause, and dependent clauses or embedded clauses which function as periphery. For the comparative study between colloquial and reading pronunciation, This research found more than 200 words which were different in terms of onset (initial consonant), rime (vowel and final consonant), tone (very few) and syllable. Selecting Chinese character for colloquial langauge, the informant emphasized the same meaning and similar meaning respectively. If a similar meaning could not be found, then the same or similar sound was selected instead. The Chinese writing system uses pictograph for characters which indicate meaning more than sound. The informant in this research knows and learns Mandarin Chinese very well so he considered the meaning of the Chinese character rather than the sound. These days, it is very difficult to find good Hakka speakers because most Hakka are assimilated into the Thai community. Therefore, the Hakka language is at risk of disappearing in the near future. If there are people interested in studying other Hakka sub-dialects in Thailand, including Hakka culture, before language data is lost, it will be useful for further academic study.