With an intention to investigate the developmental tendencies of motor ability in infants, tests of pass-or-fail type were administered. Total of 349 infants (198 boys and 151 girls), ages ranging from 4 to 6 years, were measured from Apr. 1977 through Oct. 1978, using about 39 items from "Kano's motor ability test". The test consisted of such 4 elements as (a) body balancing, (b) body coordination, (c) manual dexterity, and (d) reverse action of arms or legs, and imitating. The results may be summarized as follows: 1. The developmental tendencies of motor ability viewed from the percentage of passing in the items. 1) The ability of standing with eyes closed was generally established at the age of 4 years. About 40 % of the 6-year-olds passed in the test of standing on tiptoes with eyes open (10 seconds), and about 70 % passed in the test of single leg standing with eyes open (right and left, 10 seconds each). 2) All of the 4-year-olds passed in the test of walking on a straight line, and more than 90 % of the 5-year-olds passed in the test of one-footed skip (right and left, 5 m each). The ability of standing high jump in 20 cm was generally established at the age of 4 years. More than 95 % cleared 40 cm height at the age of 5 years and a half. All of the 6-year-old boys passed in the throwing test for accuracy with a small ball (1.5 m, pass when one hits in 3 trials). 3) The ability in drawing by use of a pencil and in manipulating a pair of scissors rapidly developed at the age of 5 years. Tapping with a pencil (30 seconds, over 110) was more than 90 % as the percentage of pass, at the age of 6 years. Bar-gripping reaction time (40 cm, pass when one grips in 5 trials) was continuously improved from 80 % till 90 % as the percentage of pass, increased from the ages 4 to 6 years. 4) Counting action on fingers was established with 100 % at the age of 5 years and a half, and action of tapping laps with hands, at the age of 4 years. 2. As a result of measuring the 39 items, the developmental tendencies of motor ability may be classified into 7 types. 3. Boys were superior to girls in many performances of ball throw, but inferior in performances of tapping and rhythmical movements of the body. 4. In comparison with the preceding study (Matsui, 1953), remarkable increase in the percentage of pass was found in jump items, but decrease was observed on items concerning body balancing.