Despite growing wealth and a strengthening government commitment to improve livelihoods and welfare, many students across rural China have inadequate access to micronutrient-rich diets. Poor diets can lead to nutritional problems, such as iron-deficiency anemia, that can adversely affect health, attention, learning, and mental health. The overall goal of this paper is to assess the impact of multiple micronutrient supplementation (MMS) on anemia and anxiety among students in poor areas of rural China. To achieve this goal, we conducted a randomized controlled trial in 54 randomly chosen elementary schools in 8 of the poorest counties in Shaanxi Province in Northwest China. Study participants were 2730 fourth-grade students, mostly aged 10-12 y. Schools were randomly assigned to 1 of 2 groups: a control group that received no intervention and an intervention group that received a daily MMS with 5 mg of iron (ferrous sulfate) for 5 mo. Our primary outcome measures were hemoglobin (Hb) concentrations (assessed by HemoCue 201+ technology), anemia prevalence (defined as Hb) concentrations ≤120 g/L), and anxiety (using a written mental health test). The results showed that 42.4% of students were anemic at baseline. The Hb concentration was 121.7 ± 10.7 g/L in the treatment group and 123.4 ± 11.4 g/L in the control group. MMS increased Hb concentrations by 1.7 g/L ± 0.15 and reduced anemia rates by 7.0 percentage points (P < 0.05). Anxiety was reduced by 0.30 SDs (P < 0.01). MMS reduced both anemia and anxiety. Our results should encourage further research on the linkages between nutrition and mental health in a development context.