ObjectiveTo assess the psychometric properties of the Thai version of the Self-Care Self-Efficacy Scale version 3.0 (SCSES-v3.0) in individuals with chronic illnesses. Although originally developed and tested in a Western context, its applicability in Asian populations, including Thailand, remains inadequately explored. MethodsPsychometric tests were guided by COSMIN principles. This included the translation of the English version into Thai based on the ISPOR framework. Nine nursing experts evaluated the content validity. Data were obtained from a multicenter cross-sectional study conducted between July and November 2022. This study included individuals with chronic conditions from 16 primary care centers in Thailand. We tested the structural validity using exploratory factor analysis (EFA) and confirmatory factor analysis (CFA), and concurrent validity in relation to the Self-Care of Chronic Illness Inventory version 4.c (SC-CII-v4.c). We tested the scale’s reliability with McDonald’s ω, Cronbach’s α, and the intraclass correlation coefficient (ICC). ResultsThe Thai SCSES-v3.0 demonstrated excellent content validity (k = 1.00). The final analysis included a total of 385 participants. The EFA with the first split-half subsample (n = 193) extracted a two-factor structure. One reflected SCSES for maintenance and monitoring behaviors and another captured SCSES for management behaviors (item 6–10). CFA with the second split-half subsample (n = 192) and the overall sample (n = 385) supported the scale’s two-factor model with high factor loadings. Each dimension and the overall SCSES-v3.0 positively correlated with each scale and the overall SC-CII-v4.c. McDonald’s ω and Cronbach’s α (both ranged 0.91–0.94) and ICC (ranged 0.95–0.96), indicated excellent internal reliability and test-retest reliability, respectively. ConclusionsThe identification of a valid and reliable two-factor model for the Thai SCSES-v3.0 renders it a valuable tool for clinicians and investigators, facilitating the assessment of self-efficacy in self-care across diverse contexts.