This study was carried out to investigate Mathematics interest as a correlate of Basic 9 students achievement in Mathematics in Gboko Metropolis, Benue State, Nigeria. Three research questions were asked and three hypotheses were formulated. The study adopted a correlation design. The population of the study was 3,682 while a sample of 400 Basic 9 students was drawn from ten secondary schools using multistage sampling procedure made up of 200 male and 200 female students. Two research instruments Maths Interest Inventory (MII) and Students Mathematics Achievement Test (SMAT) were adapted. The instruments were validated by three experts and trial-tested, on a population outside the study area. Cronbach Alpha reliability coefficient was used to get the reliability coefficient of MII which was 0.83. While that of SMAT was 0.65 using Kuder-Richardson 21 formula. The research questions were answered using Pearson Product Moment Coefficients and hypotheses were tested at 0.05 level of significance using p-values of Pearson Product Moment Coefficient. The findings of the study revealed that there was a significant relationship between Mathematics Interest and students achievement in Mathematics. Furthermore, there was a significant relationship between Mathematics Interest and students achievement in Mathematics among male and female students. The study recommends that Interest have the potential of improving students achievement positively and should be encouraged among students.Student Interest, Mathematics Achievement.