The popularity and advancement of smartphones generate a new phenomenon of smartphone addiction. To promote early identification of individuals at risk of smartphone addiction, healthcare providers could assess if an individual has nomophobia (i.e., anxiety and worry of having no smartphone at hand). The present study aimed to evaluate the psychometric properties of the Nomophobia Questionnaire (NMP-Q) across four countries: China, Bangladesh, Pakistan, and Iran. Via cross-sectional design and convenience sampling, 7871 participants (5969 Chinese, 534 Bangladeshi, 666 Pakistani, and 702 Iranian) completed the NMP-Q. Confirmatory factor analysis (CFA) and network analysis were used to examine the psychometric properties of the NMP-Q across the four countries. CFA identified a four-factor structure (Tucker-Lewis index = 0.934, comparative fit index = 0.943, standardized root mean square residual = 0.037, and root mean square error of approximation = 0.079) for the NMP-Q, and the four-factor structure was measurement invariant across genders and countries. Network analysis results supported the CFA findings via visualized correlations among the NMP-Q items. The four-factor structure of the NMP-Q was consistently found in the four countries of China, Bangladesh, Pakistan, and Iran, indicating that the NMP-Q includes four specific domains. Measurement invariance suggests the NMP-Q may effectively assess nomophobia across genders and countries.