IMPORTANCE　The　association　of　micronutrient　supplementation　during　pregnancy　with　the　intellectual　development　of　adolescent　offspring　is　unknown.　OBJECTIVE　To　assess　the　long-term　association　of　antenatal　micronutrient　supplementation　with　adolescent　intellectual　development.　DESIGN,　SETTING,　AND　PARTICIPANTS　This　14-year　follow-up　study　of　a　randomized　clinical　trial　of　micronutrient　supplementation　in　pregnancy　was　conducted　in　2　counties　in　rural　western　China　in　2118　adolescent　offspring　(aged　10　to　14　years)　of　mothers　who　were　randomized　to　take　a　daily　capsule　of　either　folic　acid,　folic　acid　plus　iron,　or　multiple　micronutrients　from　August　1,　2002,　through　February　28,　2006.　Follow-up　was　conducted　from　June　1,　2016,　through　December　31,　2016.　Data　analyses　took　place　from　April　1,　2017,　to　June　20,　2017.　MAIN　OUTCOMES　AND　MEASURES　Adolescent　full-scale　intelligence　quotient　and　aspects　of　verbal　comprehension,　working　memory,　perceptual　reasoning,　and　processing　speed　indexes　were　assessed　by　the　Wechsler　Intelligence　Scale　for　Children.　RESULTS　Of　2118　adolescent　offspring,　1252　(59.1%)　were　boys　and　866　(40.9%)　were　girls,　with　a　mean　(SD)　age　of　11.7　(0.87)　years,　representing　47.2%　of　the　4488　single　live　births　that　were　eligible　to　participate.　Compared　with　folic　acid　supplementation,　multiple　micronutrient　supplementation　was　associated　with　a　1.13-point　higher　full-scale　intelligence　quotient　(95%　CI,　0.15-2.10)　and　a　2.03-point　higher　verbal　comprehension　index　(95%　CI,　0.61-3.45);　similar　results　were　found　in　comparison　with　folic　acid　plus　iron.　When　mothers　initiated　supplementation　early　(＜12　weeks　of　gestation)　and　had　an　adequate　dose　(＞=　180　capsules),　multiple　micronutrient　capsules　were　associated　with　a　2.16-point　higher　full-scale　intelligence　quotient　(95%　CI,　0.41-3.90)　and　4.29-point　higher　verbal　comprehension　index　(95%　CI,　1.33-7.24)　compared　with　folic　acid　capsules.　The　mean　test　scores　were　lower　in　the　substratum　of　supplementation　initiated　late　(＞=　12　weeks　of　gestation)　and　with　an　inadequate　dose　(＜180　capsules).　The　multiple　micronutrient　group　had　higher　scores　than　the　other　2　treatment　groups,　and　significant　differences　were　observed　for　full-scale　intelligence　quotient　(adjusted　mean　difference,　2.46;　95%　CI,　0.98-3.94)　when　compared　with　the　folic　acid　plus　iron　group.　CONCLUSIONS　AND　RELEVANCE　Compared　with　folic　acid　plus　iron　or　folic　acid　capsules　supplementation,　antenatal　multiple　micronutrient　supplementation　appeared　to　be　associated　with　increased　adolescent　intellectual　development;　initiating　supplementation　in　the　first　trimester　and　then　continuing　for　at　least　180　days　were　associated　with　the　greatest　rewards.