Recently Vygotsky’s concept of the zone of proximal development has been drawn a great attention in the field of cognitive development. The zone of proximal development connects a psychological perspective on child development with an educational perspective on instruction. As an analytic tool for evaluation of school children’s cognitive development in connection with formal schooling, this concept of ZPD is of great value to curriculum and teachers. The aim of this paper is to formulate a theory of instruction based on Vygotsky’s theory of ZPD. He emphasized the differences among children in the level of development, and explained that children may have the same level of actual development but may be quite different in the potential level of development, thus stressing the importance of instruction accorded with that potential level of children’s cognitive development. In conclusion, this paper pointed out some instruction principles based on Vygotsky s theory of ZPD applicable for formal school instruction such as ; ① teaching according to potential development level, ② the instructional conversation, ③ the double move in teaching, ④ activity settings, ⑤ nonsupervisory assisting performance.