Objective: Mobile health has provided an effective means to educate, empower, and provide access to health services for individuals and groups. This study aimed to compare the effects of gain-frame and loss-frame SMS on the knowledge and practice of mothers with children under the age of six years regarding pediatric oral health. Research design: This randomized controlled trial was conducted in kindergartens and preschool centers of Shiraz, Iran in 2016. There were 71 mothers in the gain-frame group, 66 in the loss-frame group and 74 in the control group. The data were collected before and three-four weeks after the intervention. Data analysis used descriptive statistics, independent t-test, ANOVA, Pearson correlation test, ANCOVA, and post-hoc LSD test (Least Significant Difference). Results: There was a significant difference between the control (8.83±2.03) and gain-frame (11.8±2.17, p<0.001) and loss-frame (12.09±1.94, p<0.001) groups for post-test knowledge scores. A difference was also observed between the control group (56.27±11.53) and gain-frame (60.8±7.77, p<0.001) and loss-frame (60.25±8.96, p<0.001) groups for post-test practice scores. No difference was found between the gain-frame and loss-frame groups for the post-test scores (p=0.69). Conclusion: Gain-frame and loss-frame SMS had similar impacts on the mothers’ knowledge and practices about their children’s oral health. However, both improved the mothers’ knowledge and practice. Therefore, regardless of the style of text message framing, this method may be useful for educating mothers. Keywords: Telemedicine, Text messaging, Knowledge, Oral health, Child, Mothers