In recent years, the prevalence of smartphone addiction has significantly increased. This situation has raised concerns about its potential impact on health aspects, such as sleep quality and mental health, particularly among vulnerable populations like pregnant women. This study aimed to identify the factors that determine sleep quality in pregnant women and examine the relationship between smartphone addiction, depression, and sleep quality. This descriptive correlational study included 257 pregnant women in their second and third trimesters who were registered at six family health centers between September 2022 and March 2023. Data were collected using a sociodemographic questionnaire, the Smartphone Addiction Scale Short Form, Edinburgh Postnatal Depression Scale, and Pittsburgh Sleep Quality Index. Regression and mediation analyses were performed for the data. Of the participants, 44.4 percent had poor sleep quality. Depression and third trimester were significant determinants of sleep quality. The bootstrapping results revealed that smartphone addiction led to an increase in the level of depression (β = 0.145;  < .001). Depression worsened sleep quality (β = 0.262;  < .001). The smartphone addiction did not significantly affect sleep quality (β = 0.020;  = .279). Depression mediates the relationship between sleep quality and smartphone addiction (β = 0.038; 95 percent CI [0.018: 0.062]). The study highlights that while smartphone addiction does not directly impact sleep quality in pregnant women, it is associated with increased depression levels, which subsequently worsen sleep quality. It is recommended that healthcare providers monitor smartphone usage and mental health in pregnant women to mitigate the risk of sleep disturbances and improve overall well-being.