【Objective】 To study on the mental development status of children with phenylketonuria, to investigate the interference factors and provide guidance for clinical treatment of PKU. 【Methods】 32 children with phenylketonuria detected by neonatal screening in Qingdao were studied and compared to 46 matched normal children born at the same time. Mental development of children was evaluated by self-made inventory questionnaire and Wechsler Intelligence Scale for Children Chinese Version. 【Results】 1)No significant difference was found in Wechsler Intelligence Scale for Children Chinese Version between the time of obtaining initial treatment less than 30d group and more than 30d group(P>0.05).2)Intelligence development of children in totally cooperative group, partly cooperative group and uncooperative group had significant differences(P<0.01). 【Conclusions】 By giving strictly low-phenylalanine dietotherapy to keep ideal phenylalanine levels is a key to mental development of children with PKU. Developing treat cooperativity plays an essential role in it which must be done so the children with PKU could grow healthy.