BACKGROUND Excessive or insufficient gestational weight gain (GWG) is associated with increased risks of pregnancy complications and adverse delivery outcomes in dichorionic twin pregnancies. The provisional Institute of Medicine (IOM) 2009 guidelines suggested the optimal GWG based on limited epidemiological data collected from Western populations. However, such a recommendation has not yet been validated in a Chinese Han population, the world's largest ethnic group. The objective of this study was to assess the effect of IOM guidelines by determining the neonatal and maternal outcomes associated with gaining weight below, within, and above the IOM provisional guidelines on GWG in Chinese Han twin pregnancies. MATERIAL AND METHODS A historical cohort study of 350 twin-conceiving Han women in Chongqing Women and Children's Health Center delivering liveborn twin infants between January 2015 and November 2016 was conducted. The participants were divided into 3 groups according to the 2009 Institute of Medicine recommendations of GWG: a low GWG group, an adequate GWG group, and a high GWG group. The incidence of pregnancy complications and the delivery outcomes were compared between the groups, and the correlation of GWG and pregnancy complications or delivery outcome was investigated by logistic regression analysis. RESULTS In Han Chinese people, the gestational age (GA) at delivery was significantly different among various GWG groups, and low maternal GWG is associated with shorter GA. Although low GWG increased the incidence of VPTD, it did not impact PTD in twin pregnancies. Moreover, GWG was negatively correlated with the incidence of PPROM and was positively correlated with GHP development in twin pregnancies. CONCLUSIONS The recommendations of the 2009 IOM guidelines about GWG is beneficial in reducing the incidence of VPTD and PPROM in Han Chinese dichorionic twin pregnancies, but failed to eliminate the development of PTD, PROM, GDM, PE, ICP, and SGA.