The seminal root tips of the rice, var. Norin No. 29 were used as materials. Two root tips were grown in each flask containing 15 ml of liquid medium. Cultures were maintained at 26∼27°C in the dark for the periods from half to one month, until the root growth ceased. The following subjects were studied. First, the effects of yeast extract, peptone, casamino acid (casein acid hydrolysate), tryptophane and indole acetic acid on the growth of excised root tips have been investigated. These substances were added singly or in combination to the basic components of medium, i. e., modified White's inorganic salts (containing 0.4 mg per liter of Fe in the form of ferric citrate) and sucrose or dextrose. Among the substances tested, casamino acid were most stimulating to the growth of root tips. Other substances were without noticeably favorable effects. Basing upon these results, the "original medium" were obtained, which was consisted of modified White's inorganic salts, 4 percent sucrose and 0.2 percent casamino acid. Next, the several factors involved in the preparation of the "original medium" have been examined to study their respective effects on the growth of excised roots. The points which have emerged from these experiments were as follows: i. the optimum PH of the medium is . 4.0, ii. the concentration of Fe may be increased to 4.0 mg per liter, iii. the optimum concentration of sucrose is relatively high, about 6 percent, and iv. the autoclaving of the medium at 1.0 kg per cm² air pressure for five minutes shows best results. In addition to these, it was found that the vitamins (thiamin, pyridoxine and nicotinic acid each in the concentration of 0.5 mg per liter) accelerated the growth of excised root tips distinctly unless they had been sterile-filtered. By all accounts, "improved medium" were constituted as follows: modified White's inorganic salts (containing 4.0 mg per liter of Fe in the form of ferric citrate), 6 percent sucrose, each 0.5 mg per liter of thiamin, pyridoxine and nicotinic acid and 0.2 percent casamino acid. Superiority of the "improved medium" to the "original medium" for the growth of excised root tips of rice were verified. Nevertheless, incapability of "improved medium" to sustain the unlimited growth of excised rice roots were the problem remaining for future work.