Objective: This study was aimed to compare serum galectin-3 (Gal-3) levels in gestational diabetes mellitus (GDM) and healthy pregnant women and to evaluate the relationship between insulin resistance parameters and serum Gal-3 levels. Materials and Methods: Fifty-nine pregnant women who were screened for GDM with oral glucose tolerance tests (OGTT) at the 24th-28th gestational weeks were included in the study. According to the results of OGTT, 34 pregnant women were included in the GDM group and 25 pregnant women were included in the control group. Results: Serum Gal-3 value was found to be similar in the GDM and control group (P < 0.471). However, there was a significant positive association between Gal-3 and fasting insulin (r = 0.509, P < 0.001) and homeostasis model assessment of insulin resistance (HOMA-IR) (r = 0.479, P < 0.001) in the whole pregnancies, and between Gal-3 levels and fasting insulin (r = 0.608, P < 0.001), HOMA-IR (r = 0.609, P < 0.001), and OGTT 60 min glucose (r = 0.444, P = 0.016) in the GDM patients. Conclusions: There was no difference in the last trimester serum Gal-3 levels between GDM and healthy pregnant women. However, a significant positive correlation was determined between Gal-3 and fasting insulin, HOMA-IR, and OGTT 60 min glucose values in the GDM group, and fasting insulin and HOMA-IR values in whole pregnancies. The results of our study support previous data reporting the relationship between Gal-3 and GDM through insulin resistance.