Introduction: Child's vocabulary increases with age and knowing its growth is important for research and clinical purposes. This study aimed to determine the most frequent words and lexical categories in Azari-speaking children aged from 18 to 24 months. Also the lexical development trend up to 24 months was studied. 

Methods: This longitudinal study was conducted on 17 18-24 month old Azari-speaking children selected by the cluster sampling method from Tabriz’s kindergartens and lasted for 6 months. The tools for the collection of data included weekly children's vocabulary sheet and vocabulary lists. The data were analyzed using descriptive statistics.

Results: Among 279 words, 31 words were used in the first week of 18 months. Childlike words: foods and stereotypes were the most used words. Childlike words made the largest category and animal words made the smallest category. Thirty seven words met the age of acquisition criteria during 6 months that the childlike category with 11 words was the largest and grammatical words and location categories each with 1 word were the smallest categories.

Conclusion: Considering that childlike words are most used compared to other categories, it can be concluded that children, at first, learn words that are easier pronounced and expressive lexicon size and variety of its categorizes increase by age increase.