To prevent and treat hypertension, it is important to restrict salt in one's diet since adolescence. However, an effective salt-reduction education system has yet to be established. Besides accurate evaluation, we believe that the frequent usage of a measurement device may motivate individuals to avoid high salt intake. The present study evaluated the use of a urinary salt excretion measurement device for salt-reduction education in a parallel randomized trial of two groups. The sample comprised 100 university students who provided consent to participate. A survey with 24-hour home urine collection and blood pressure measurement was conducted. Participants in the self-monitoring group measured their own urinary salt excretion level for 4 weeks, using the self-measurement device. Analyses were conducted on 51 participants in the control group and 49 in the self-monitoring group. At baseline, there was no significant difference between the two groups in terms of their characteristics and 24-hour urinary salt excretion levels. After intervention, 24-hour urinary sodium/potassium ratio showed no change in the control group [baseline score: 4.1 ± 1.5; endline score: 4.2 ± 2.0; P = 0.723], but it decreased significantly in the self-monitoring group [baseline score: 4.0 ± 1.7; endline score: 3.5 ± 1.4; P = 0.044]. This change was significant even after adjusting for baseline and endline differences between groups using analysis of covariance (P = 0.045). The self-monitoring urinary salt excretion measurement device improved the 24-hour urinary sodium/potassium ratio. The device is a useful and practical tool for educating young individuals about dietary salt reduction.