Anemia and co-existing deficiencies of zinc, iron, iodine, and vitamin A occur among children in many developing countries including NE Thailand, probably contributing to impairments in growth, immune competence, and cognition. Sustainable strategies are urgently required to combat these deficiencies. We assessed the efficacy of a micronutrient-fortified seasoning powder served with a school lunch on reducing anemia and improving the micronutrient status of rural NE Thai children. Children (n = 569) aged 5.5-13.4y from 10 schools were randomly assigned to receive a seasoning powder either unfortified or fortified with zinc (5 mg), iron (5 mg), vitamin A (270 microg), and iodine (50 microg) (per serving) and incorporated into a school lunch prepared centrally and delivered 5 d/wk for 31 wk. Teachers monitored school lunch consumption. Baseline and final micronutrient status, hemoglobinopathies, and infection or inflammation were assessed from blood and urine samples. For the primary outcome, anemia (based on hemoglobin), no intervention effect was apparent (odds ratio: 1.02 95% CI: 0.69, 1.51) after adjustment for design strata. The odds of zinc (based on serum zinc) and urinary iodine deficiency in the fortified group were 0.63 (0.42, 0.94) and 0.52 (0.38, 0.71) times those in the unfortified group, respectively. Fortification had no effect on serum retinol (0.61: 0.25,1.51), ferritin (1.12: 0.43, 2.96), or mean red cell volume (1.16: 0.82, 1.64). Therefore, a micronutrient-fortified seasoning powder is a promising vehicle for improving zinc, iodine, and hemoglobin status, and its potential for incorporation into lunch programs in day care centers and schools in NE Thailand warrants investigation.