The aim of this cross-sectional study was to investigate the discriminant validity of the Persian version of Alberta Language Development Questionnaire (ALDeQ) in Turkish-Persian bilingual children, aged 75 months with 19 months of exposure to Persian, on average. The study sample included the parents of 22 bilingual children with language impairment (LI) and 114 with typical language development (TLD). The T-test results showed significant between-group differences regarding ALDeQ total scores, and for each section score, with medium to very large effect sizes. The linear discriminant function analysis showed the ALDeQ total score was a moderate to strong discriminator between TLD and LI group. The sensitivity and specificity of the questionnaire were 0.80 and 0.89, respectively. The Persian version of ALDeQ is an appropriate tool for assessing the language development of Turkish-Persian bilingual children and can be used in conjunction with other measures to identify children suspected of LI.