This cluster-randomized controlled trial study aimed to assess the effectiveness of the interactive multi-modality technology (IMM) as an intervention to increase self-management among type 2 diabetic patients in a 3-month period. The IMM intervention contained email, Short Message Service (SMS), and website with four main functions (i.e., self-regulation, self-monitoring and assessment, social support, and reminder system—linked to email and SMS). In this trial, four public offices in the Bangkok Metropolis were recruited and randomly assigned into either the intervention or the control group. One hundred and twenty-six Thai patients who had met inclusion criteria (hemoglobin A1c or A1c >7.0 %, no serious illness, and Internet and mobile phone accessibility) were subsequently assigned to the intervention (n = 78) and the control (n = 48) groups. Patients in the intervention group received the IMM intervention. Those in the control group received self-management knowledge via email only. Outcome measures, A1c, and behavioral questionnaires (Diabetes Quality of Life, Self-efficacy, and Self-care Management) were applied to all patients at baseline and at 3-month follow-up. T test and chi-square test were used to analyze the data. After 3 months, 55 (out of 78) and 30 (out of 48) patients remained in the study. Main findings revealed a significant difference in A1c level between the groups (p < 0.001). The self-care management score increased in both groups, but the increase was significantly higher in the intervention group (p < 0.001). For the first time, this demonstrates the effectiveness of the IMM intervention among type 2 diabetic Thai patients with computer literacy.