This study aimed at comparing the effect of two test item formats (multiple-choice and complete) on estimating person's ability, item parameters and the test information function (TIF).To achieve the aim of the study, two format of mathematics(1) test have been created: multiple-choice and complete, In its final format consisted of (31) items. The test has been applied on (300) students in Tabuk University. The responses of the examinees were analyzed by BILOG-MG 3 programs for each item form according to the two parameter logistic model. The study findings revealed the following: there were statistically significant differences at the level of significance ([alpha]=0.05) among the standard error means for estimating item parameters (difficulty and discrimination) due to the format of test item in favor of the complete test. And the results showed there were statistically significant differences at the level of significance ([alpha]=0.05) among the standard error means for estimating person's ability due to the format of test item in favor of the complete test. On the other hand, the results showed there were statistically significant differences ([alpha]=0.05) among the standard error means of test information function (TIF) due to the format of test item in favor of the complete test. The study recommends educating teachers to diversify the forms of items of the tests they use so that they contain the two forms (multiple-choice and complete), and using complete items on a larger scale. than it is now being more discrimination.