To investigate whether an intervention including micronutrient-fortified complementary foods can improve iron status, we conducted a randomized controlled trial in 5-mo-old Vietnamese infants (n = 246). Villages (n = 29) were randomly divided into those receiving instant flour (FF) or a food complement (FC) both fortified with micronutrients or nothing [control (C)]. FF and FC infants received daily for 6 mo at least 2 meals of fortified complementary foods. Micronutrient status was assessed by measurement of hemoglobin (Hb) and plasma ferritin (PF), transferrin receptor, zinc, and retinol. Final Hb (mean ± SD) was higher in the FF (112.5 ± 8.0 g/L) and FC (114.0 ± 7.0 g/L) groups compared with C (109.0 ± 8.0 g/L; P = 0.006). PF (geometric mean [95% CI]) was also higher in FF (19.8 μg/L [17.5-22.3]) and FC (20.8 μg/L [18.3-23.6]) compared with C (11.1 μg/L [9.8-12.5]; P < 0.0001). Anemia prevalence decreased more in the FC group (-43.6%) compared with C (-10.3%; P = 0.006). The change in prevalence of PF < 12 μg/L was different in the FF (-16.4%) and FC (-6.7%) groups compared with C (+30.4%; P < 0.01). Endpoint prevalence of iron deficiency (ID) and ID anemia (IDA) were lower in the FF (13.4 and 6.7%, respectively) and FC (15.2 and 3.8%) groups compared with C (57.5 and 37.5%) (P < 0.0001). Retinol and zinc concentrations did not differ among groups, but endpoint prevalence of zinc deficiency was lower in FF infants (36.1%) than in C infants (52.9%; P = 0.04). Micronutrient-fortified complementary foods significantly improved iron status and decreased the prevalence of anemia, ID, and IDA in Vietnamese infants and can be an important tool to reduce ID in infancy in developing countries.