This study aimed to detect the person misfit for eight grade students in the Sultanate of Oman using the Between Squared Residual Index over sections of TIMSS2019 Mathematics test (content, cognitive levels, item format and item difficulty) and to compare by students' gender variable. This study also aimed to compare the results of the Between Squared Residual Index over Mathematics test sections with the results of the Squared Residual Index over item level. The assumptions of the three-parameter model in the item response theory were examined based on the item parameters estimated by the International Association for theInternational Association for the Evaluation of Educational Achievement (IEA). Certain functions in R programming language were used to calculate the number of students with misfit responses according to the Between Residual Square Indices (weighted and unweighted versions), and the Residual Square Indices (weighted and unweighted versions). SPSS was also used to perform a chi-square test to identify the differences between males and females in the number of misfit responses. The results of the study indicated that the percentage of students with misfit responses ranged between (2.16% & 3.22%) and between (2.13% & 3.88%) according to the (unweighted and weighted) Between Residual Square Indices respectively, while their percentage amounted to only 0.30% & 0.95% according to the (unweighted & weighed) Square Indices respectively. The results showed that most of students ' abilities with misfit responses in the Math test in TIMSS2019 ranged between low and medium. The results of the study also showed that males have more misfit responses than females in more sections of the TIMSS2019 math test. The study recommended conducting studies to determine the reasons for the presence of misfit responses in Mathematics tests in TIMSS among students of the Sultanate. It also recommended directing teachers and those in charge of applying TIMSS tests to train students in the basic mathematical skills they need to reduce behaviors that lead to misfit responses.