Abstract: Objective To investigate the genetic and environmental factors influencing juvenile's psychological and behavioral development based on the psychological and behavioral development status of twins aged 11 to 17 years.Methods A Youth Self Report(YSR)questionnaire survey was conducted in 210 pairs of twins aged 11 to 17 years in Ji'ning.Results The score of the twins was lower than that of ordinary children for questions concerning psychology and behavior.For questions related to syndromes,except for discipline-disobeying symptoms,scores of the twins increased with age and the score of self-assessment in boys was higher than that of the girls.The results of statistical analysis indicated that the factors of disciplinary offence(t=2.569,P=0.011),a ttack s(t=2.665,P=0.008)and extraversion(t=2.927,P=0.004)were different between the boys and girls.The heritability of symptoms as flinching,complaining,agitation,depression,socializing,thinking,attention,discipline disobeying,attacking,introversion and extroversion was 0.085,0.159,0.054,0.043,0.126,0.002,0.086,0.076,0.001 and 0.081,respectively.Conclusion The incidence of physical development and psychological and behavioral problems in twins is lower than that of ordinary children,and the environment is the main influential factor of psychological behavior.