Purpose : To find out deaf pupil's ability to use auxiliary words and verbs which is an important element in their development of the Japanese language, and to seek suggestions to the planning of instruction for them. Procedure : Performance test of sentences which are to be filled up with auxiliary words and verbs was given to 179 secondary deaf school pupils (53 lower secondary, 126 upper secondary pupils) and 197 secondary hearing school pupils (98 lower secondary, 99 upper secondary pupils). The ratios of the correct use of each auxiliary word and verb were brought out and distributed into five step intervals. Abstruct of the result : 1. In deaf groups, most of ratios of the correct using of each auxiliary word falled into 0-20.0 step interval, and few of them entered in 60.1-80.0 or 80.1-100 step intervals. On the other hand, in hearing groups most of the ratios entered in 80.1-100 step interval and few of them falled in 0-20.0 step interval. 2. Most of ratios of the correct using of each auxiliary verb were scattered in 0.-20.0 step interval or 20.1-40.0 step interval in deaf groups and the ratios which entered in 60.1-80.0 or 80.1-100 step interval were far more in hearing groups than in deaf groups. 3. Therefore, such ability of lower and upper secondary deaf school pupils tend to be inferior to that of hearing pupils of the first grade of lower secondary school. 4. Errors of deaf pupils at the test of auxiliary words are caused by (a) imperfect discrimination of surd sound and sonant. (b) omission of letter. (c) hypermetre (d) imperfect consideration to the connection of words. (e) using of other parts of speech. (f) immatureness of ideas. (g) to seize partially the line of thought. (h) subjective embellishment to the line of thought.