We observed the aerenchyma formation in rice primary root and compared the images obtained by paraffin section and freehand section methods. The results showed that, both of the section types were able to display the structure of rice root and the formation of aerenchyma tissue clearly. The aerenchyma in roots of 4-d old rice seedlings began to form after 24 h growth, and came to completely mature by 72 h. The more closer to the root basal portion, the more mature of the tissue, consequently the higher degree of the aerenchema development. Compared to paraffin section method, the freehand section method is more suitable for observation of the architecture of aerenchyma in rice root. Aerenchyma production in rice and wheat root upon hypoxia observed by freehand section method showed that hypoxia can significantly induce aerenchyma formation in wheat roots, whereas the promoting function in rice roots is not significant.