Dry seeds of rice and green pepper were carried in the basket of a high altitude balloon to 30-40 km for 8 h. The treated seeds were planted on the ground and characters of these seeds and their progenies, such as development, fruiting, disease resistance were observed. The results showed that the SP2 generation of the treated rice showed strong mutation. A Japonica male fertility restorer rice line was found out. It could be hybridized with sterile line of Indica rice, and their progeny had strong hybrid vigor, high setting percentage and good plumpness of grain. Disease resistance, high-yield, big-fruit and high vitamin C content strains were selected from the progenies of treated green pepper seeds. The above results indicated that the special conditions in high altitude could produce a variety of mutations and most of them are hereditable. Therefore, high altitude balloon flight can be used as a new method of mutation breeding.