Technological advances have created the environment for Internet addiction (IA). A specific form of IA is social media addiction. Moreover, social media addiction may be further classified into general or specific social media addiction, with YouTube addiction among the latter because YouTube is viewed as a video streaming application. The present study aimed to design an instrument assessing YouTube addiction (named as the YouTube Addiction Scale, YAS) for psychometric testing. Guided by the component model of addiction, the YAS included six items corresponding to salience, mood modification, tolerance, withdrawal, conflict, and relapse. Through an online survey, the first sample (N = 530; 50.6% female) completed the YAS together with other measures assessing general social media addiction, psychological distress, and demographic information. Afterward, a second sample (N = 512; 45.5% female) completed the YAS in another period of time. The YAS was found to be unidimensional with strong factor loadings in both exploratory factor analysis (the first sample) and confirmatory factor analysis (the second sample). Internal consistency of the YAS was acceptable for both samples. Using the first sample's data, Rasch models suggested that the six items in the YAS all fit well in the embedded construct of YouTube addiction. No differential item functioning was displayed for all YAS items across age, gender, and weekly time spent using YouTube. Network analysis results showed that the YAS items grouped together and had a clear distance from all items assessing general social media addiction. In addition, participants with higher levels of YouTube addiction had significantly greater general social media addiction, psychological distress, and time spent on YouTube. The YAS has promising psychometric properties for healthcare providers and researchers to assess individuals' YouTube addiction levels. Future studies should examine the extent to which with the use of YAS, healthcare providers may monitor the severity of individuals' YouTube addiction and provide early intervention, if needed.