Background There is growing interest in using social media to improve pregnant women’s well-being. This study aimed to evaluate the effects of social media (Snapchat) dissemination of health-promoting interventions on knowledge of oral health during pregnancy among pregnant women in Saudi Arabia. Materials and methods Using a single-blinded parallel group randomized controlled trial design, 68 volunteers were assigned to either a study group (SG) or a control group (CG). The SG received information about oral health during pregnancy via Snapchat, while the CG received the same information using WhatsApp. The participants were assessed three times: T1 prior to the intervention, T2 immediately following the intervention, and T3 as a follow-up 1 month later. Results A total of 63 participants completed the study in the SG or CG. According to paired t-test, total knowledge scores in the SG and CG increased significantly from T1 to T2 (p < 0.001) and from T1 to T3 (p < 0.001), but there was no significant change from T2 to T3 in either the SG or CG (p  =  0.699 and p  =  0.111, respectively). Using t-test, no significant differences were found between the SG and CG at T2 (p  =  0.263) or T3 (p  =  0.622). Also using t-test, no significant differences were found in the scores of the SG and CG from T2 to T1 (p  =  0.720), T3 to T2 (p  =  0.339), or T3 to T1 (p  =  0.969). Conclusions Using social media (e.g., Snapchat and WhatsApp) as a health-promoting intervention is a promising method for improving women’s knowledge about oral health during pregnancy for short term. However, further studies are needed to compare social media with conventional standard lecturing methods. also, to assess the longevity of the impact (short or long term).