Background:Women diagnosed with gestational diabetes mellitus suffer from anxiety and depression, which make controlling blood glucose levels difficult.Introduction:This quasi-experimental study uses a nonequivalent control group pretest-posttest design to investigate the effects of a web-based self-care program on self-care behaviors, anxiety, depression, and blood glucose in patients with gestational diabetes mellitus.Methods:The subjects of the study were outpatients being treated in the Department of Endocrinology at Hospital G, located in Seoul near University C, from July 15, 2015, to December 31, 2016. The experimental and control groups contained 22 participants each. The experimental group received a 12-week web-based program and one session of nutrition education; the control group received nutrition education. Using the SPSS program, pre-post changes in blood glucose, anxiety, depression, and self-care behaviors were examined between the two groups by a repeated-measures ANOVA.Results:After the 12 weeks intervention, self-care behaviors increased in both groups, and blood glucose monitoring increased in the experimental group (p = 0.001). Anxiety in the experimental group decreased by 5.1 points but increased by 1.0 point in the control group (p = 0.048). Depression increased in both groups. Glycated hemoglobin (HbA1C) levels decreased in the experimental group but increased in the control group (p = 0.001).Discussion:In addition to reducing HbA1C and anxiety, the web-based self-care program was effective in increasing the frequency of daily blood glucose monitoring in patients with gestational diabetes mellitus.Conclusions:This study will be helpful in informing an anxiety intervention program, blood glucose control, and healthy self-care behaviors in women with gestational diabetes mellitus.