Abstract: In order to clarify the rules of POD isoenzyme in the hazelnut, identify their blood relations between female, male and filial generations and select the superior parents for cross-breeding, we have studied the characteristics of peroxidase isoenzyme which are distributed in the 34 hazelnut varieties or lines by polyarclamide gel electrophoresis, The results showed that：POD isoenzymes of Corylus heterophylla Fisch, Corylus avellana L, and the hybrid of Corylus heterophylla Fisch × Corylus avellana L had obvious difference; some hybrids had lost P10 spectrum band of parents; the enzyme spectrum of 32 hybrid hazelnuts produced ‘new hybrid spectrum bands’that could be considered as a mean to identify hybrids.The picture of the relationship between 34 cultivars or lines in hazelnut was made by system clustering method. On the basis of the picture, the majority of hybrids showed the close relation to Corylus avellana L. and the distant relation to Corylus heterophylla Fisch. The distances of 83-63 and Corylus avellana L,84-72 and Corylus avellana L were minimum, the blood relations of 83-63、84-72 and Corylus avellana L were the closest. They were superior parents in the selected varieties for cross-breeding