The present study was conducted to investigate the capacity of the application of the item content logic analysis and the person characteristic curve to ability measurements. A total of 429 seventh and eighth graders served as examinees. The verbal comprehension test and the block counting test, two subtests of the Army General Classification Test in the Chinese revision, were administered to all subjects. The major findings are as follows: (1) The degree of difficulty in the block counting test item depends upon the way in which the figures of blocks are arranged or printed. (2) The person characteristic curve gives information whether a test measures a single ability. (3) The restricted group has no influences on the application of the person characteristic curve. (4) A few items with high indices of discrimination (larger than .30) still maintain the characteristics of a test. The author suggests that test users and writers should: (1) Adopt a variety of methods to find those factors that cause difficulty in test items with a view to defining exactly the ability which a test is claimed to measure. (2) Make use of the person characteristic curve to determine whether a test masures a single abiliy for the sake of construct validity. (3) Employ the person characteristic curve to further improve the administration of a test.