Feeding a group of albino rats with diets containing spinach 10% and another group with diets containing Itadori (Polygonum Reynoutria Makino) 10% both as calcium sources, we compered the results of hone calcification in the two groups. As the results are shown in table, the spinach group is inferior to the Itadori group. Spinach has been found to contain relatively large amounts of oxalic acid which interfere with the utilization of calcium. As the next experiment, the calcium of radish (Japanese) leaves was compared with that of spinach. The radish leaf group showed good results of calcification of bones irrespective of the amount of content in diets, but the spinach group showed worse results with the increase of the content of spinach in diets. When a variety of spinach containing a relatively small amount of oxalic acid was used, the interference was reduced. Thus it has been found that calcification of bones in albino rats fed with green vegetables depends on the amount of oxalic acid contained therein, and when the content of oxalic acid in spinach was over 1% of the diet, a worse result was obtained.