Background: The Mullen Scales of Early Learning (MSEL) is a standardized comprehensive developmental assessment tool for children aged 0–68 months. However, few Asia-based studies have explored cultural and linguistic adaptations of the MSEL or investigated its psychometric properties in populations with autism spectrum disorder (ASD). Aims: This study evaluated the reliability and validity of the MSEL-Taiwan version (MSEL-T) for Taiwanese children with ASD, global developmental delay (GDD), and typical development (TD). Methods and procedures: The MSEL items were translated and modified according to the language and culture in Taiwan. In total, 191 children (ASD, 69; GDD, 36; and TD, 86) aged 19–68 months were assessed using the MSEL-T and Peabody Developmental Motor Scales 2 (PDMS-2) at enrollment, followed by the assessments of Vineland Adaptive Behavior Scale-Chinese version (VABS-C) at the age of 36 months or later. Outcomes and results: All subscales were verified to have good interrater reliability and internal consistency, and subscale scores indicated moderate to high correlations with PDMS-2 and VABS-C scores. Significant differences in MSEL-T scores were observed between same-aged pairs of children with TD and GDD and between pairs of children with TD and ASD. Conclusions and implications: The findings provide evidence of validity and reliability of the MSEL-T. And it is suggested that the culturally and linguistically adapted MSEL-T is a good tool for the clinical assessment of children with and without ASD.