The influence of root zone temperature to the induction of inflorescence and growth of Phalaenopsis was investigated. Root zone temperatures were 15, 20, 25, and $30^{circ}C$, while the air temperature was kept over $28^{circ}C$ during three months. $CO_2$ uptake, fresh weight, dry weight and branched root number of Phalaenopsis were highest at $25^{circ}C$ and lowest at $15^{circ}C$. But, the anthocyanin content was highest at $15^{circ}C$ and lowest at $25^{circ}C$. Inflorescence was not induced by root zone cooling temperature below $25^{circ}C$ for three months. The concentrations of K, Ca and Mg in leaves were changed according to the root zone temperature, but those of N and P were not changed. K content was high at $20^{circ}C$, whereas Ca and Mg contents were high at $25^{circ}C$ root zone temperature. This study indicates that Phalaenopsis perceives temperature by shoot and the optimum root-zone temperature for the vegetative growth is $25^{circ}C$.