AIM: To investigate the association between tear film break up time (TBUT) and blinking interval in visual display terminal (VDT) users. METHODS: Nine hundred and thirty VDT users underwent dry eye testing, and functional visual acuity (FVA) test. The blinking interval during FVA was compared with TBUT. Subjects with longer blinking interval than TBUT were considered as unstable tear film. Logistic regression analysis revealed the risk factors for unstable tear group. RESULTS: Among 930 workers, 858 subjects (92.3%) participated in this study. Almost 80% of the subjects were categorized into the unstable tear group. Unstable tear group has significantly lower Schirmer values and TBUT (17.5±11.6 vs 21.1±11.5 mm, 3.7±2.6 vs 5.7±2.7s, both P<0.001). There were no significant differences in epithelial staining or severity of symptoms. Logistic regression showed that over 40y was a risk for being unstable tear group [odds ratio (OR)=1.53; 95% confidence interval (CI)=1.06-2.20]. Contact lens use was protective factor for being in the unstable tear group (OR=0.37; 95%CI= 0.26-0.53). CONCLUSION: Subjects with shorter TBUT than blinking interval are prevalent among VDT users. Subjects over the age of 40 shows an increased risk for unstable tear film.