This study aimed to adapt and validate the Word Complexity Measure (WCM) for Persian-speaking toddlers. The WCM is a tool for assessing phonological complexity, originally proposed by Stoel-Gammon. The study was conducted in two phases: (1) adapting the WCM parameters to the Persian language and (2) conducting a validation study with 60 monolingual Persian-speaking toddlers aged 18-35 months. The toddlers' language productions were collected through a picture-naming task, and the researchers derived the Proportion of Word Complexity Measure--Persian (PWCM-P) and Proportion of Consonant Correct (PCC) scores. Parents completed the Persian adapted version of the MacArthur-Bates Communication Development Inventories--II (CDI-II) to obtain receptive and expressive vocabulary scores for each child. Statistical analyses showed a significant difference in PWCM-P scores between age groups, with younger children producing fewer phonologically complex words. In addition, PWCM-P scores were positively and significantly correlated with PCC scores, receptive and expressive vocabulary size. Overall, the successful adaptation and validation of the WCM for Persian provides a reliable tool for assessing phonological development in young children and sheds light on the importance of phonological complexity in vocabulary acquisition. This research can further deepen our understanding of phonological development during early childhood and its implications for language learning.