Abstract: Two varieties of ball cactus (Melocactus and Notocactus) were grown in hydroponics with four nutrient solution formulae and in a peatmoss medium culture as control, respectively, to study the growth and the adaptability of ball cactuses in hydroponics. The results showed that both of the tested ball cactuses varieties could grow well in hydroponics, in which the growth rate was significantly higher than or equal to that in medium culture. Melocactus grew best in formula 2 with a little of NH~+_4-N, but Notocactus grew well in all of the tested formulae with or without NH~+_4-N, the higher content of NH~+_4-N in the nutrient solution might be harmful to the growth of Notocactus. The pH value of the nutrient solutions decreased after the NH~+_4-N was added. But the low pH value would not influence the growth of the ball cactuses. It implied the two varieties of ball cactuses were tolerant to low pH conditions.