We investigate the relationship of diabetes knowledge, diabetes management self-efficacy and diabetes self-management with blood glucose control among people with Thai type 2 diabetes mellitus (T2D). Seven hundred outpatients from diabetes clinics from large university and small community hospitals in two provinces of Thailand (Khon Kaen and Bangkok) were interviewed to evaluate their diabetes knowledge (DK), diabetes management self-efficacy (DMSE) and diabetes self-management (DSM). In addition, patient medical records were accessed to obtain other patient characteristics including patients' HbA1c levels. Bivariate and multivariable logistic regression modelling was conducted and unadjusted and adjusted odds ratios obtained, respectively. Over half (52.4%) of the patients in our sample failed to control their blood glucose (HbA1c > 7%). All three psychometric measures (DK, DMSE and DSM) were identified as associated with blood glucose control in the bivariate analysis (ORDK(unadj) = 0.89, 95%CI: 0.82, 0.96; ORDSM(unadj) = 1.64, 95%CI: 1.46, 1.82; ORDMSE(unadj) = 2.84; 95%CI: 2.43, 3.32). However, after mutual adjustment and adjustment for other patient characteristics, of the three psychometric measures, only diabetes management self-efficacy remained associated with blood glucose control (ORDMSE(adj) = 2.67; 95%CI: 2.20, 3.25). Diabetes management self-efficacy is shown to be strongly associated with blood glucose control in the Thai Type 2 diabetes population. Current early diabetes interventions in Thailand tend to focus on disease knowledge. A stronger emphasis on enhancing patients' disease management self-efficacy in these interventions is likely to lead to substantial improvement in both diabetes self-management and blood glucose control, thereafter reducing the risk, or prolonging the development, of chronic diabetes complications.