Abstract: Objective To explore the characteristics of behavioral development and its relationship with mental and psychomotor development among rural 30-month-old infants in Shaanxi province.Methods Totally 977 rural infants born between 2002 and 2006 in 2 counties in Shaanxi province were followed up retrospectively and their mental,psychomotor,and behavior development at the age of 30 months were assessed by using Bayley Scales of Infant Development(BSID).Exploratory factor analysis was performed to extract the major factors.Spearman and partial correlation were used to evaluate associations of mental and psychomotor development with behavioral development.Results The 30-month-old infants had relative higher scores for cooperativeness (3.9±0.8),emotional tone (4.1±0.6),object orientation (3.9±0.7),endurance (4.1±0.5),and sights (3.9±0.5),but lower scores for fearfulness (1.7±0.8),tension (2.5±0.6),and sucking thumb or fingers (1.1±0.5),respectively,suggesting the enhanced positive emotion and declined negative emotion among the infants.Exploratory factor analysis revealed 6 common factors (activity,social adaptability,concentration,endurance,motor coordination,and affinity) associated with mental development index (MDI) and the 6 factors accounted for 56.77%variation of MDI,with the adjusted correlation coefficients ranging from 0.081 to 0.359;however,of the 6 factors only 4 (activity,concentration,endurance,and motor coordination)were significantly correlated with psychomotor development index (PDI),with the adjusted correlation coefficients of from 0.080 to 0.475.In all of behavior factors,activity factor was most closely correlated with MDI and PDI.Conclusion Well developed behavior is positively associated with MDI and PDI.Early education and intervention targeted on abnormal infant behavior could help to improving infant behavior development,cognitive abilities and motor skills.