Background: Dry eye syndrome is one of the complaints of diabetic patients. The aim of the present study was to evaluate the tear functions in pregnant women with gestational diabetes mellitus (GDM) using tests: Schirmer, tear break-up time (TBUT), and tear film osmolarity (TFO) tests and the Ocular Surface Disease Index score (OSDI). Methods: Pregnant women with GDM (Group 1, n=46) and healthy pregnant women (Group 2, n=36) were enrolled. Initially, all participants were asked to answer the OSDI and then they underwent a detailed ophthalmic examination including Schirmer, TBUT, and TFO tests. The individuals with ocular or systemic disorders that might affect the tear function tests and who were using topical medications were excluded. Results: The results of Schirmer, TBUT, TFO tests and OSDI scores were 11.20 +/- 4.93 mm, 5.59 +/- 2.16 sec, 309.65 +/- 14.80 mOsm/L, and 9.59 +/- 9.69 in Group 1, respectively, and 12.33 +/- 5.33 mm, 5.67 +/- 2.68 sec, 308.36 +/- 16.00 mOsm/L, and 10.62 +/- 8.66 in Group 2, respectively. There was no significant difference in any of the tear function tests and OSDI scores between the study groups (p>0.05). Conclusion: GDM seems to have no negative effects on tear function tests. This may be due to a lack of duration of hyperglycemia long enough to affect the tear function tests of pregnant women.