This study was a non-experimental design that incorporated Pearson Correlation, multiple regression and stepwise regression: (a) to investigate the statistically significant relationship between of spatial and fluid intelligences and mathematical abilities in ninth and tenth grade high school students, and (b) to assess which predictor variable, fluid or spatial intelligence, was the best predictor of mathematical abilities. The sample consisted of 109 high school students, 55 females and 54 males, enrolled in either Spectator Hall Academy or Hillside Valley Academy, two private religious high schools located in a small Northeastern state. The Revised Minnesota Paper Form Board Test (RMPFBT) was used to assess spatial intelligence, the Ravens Progressive Matrices (RPM) was used to assess fluid intelligence, and the Test of Mathematical Abilities, Second Edition (TOMA-2) was used to assess mathematical abilities. The correlation between RMPFBT scores and TOMA-2 scores was .18 (p < .05) indicating a relatively low, but statistically significant, correlation between spatial intelligence and mathematical abilities. The correlation between RPM scores and TOMA-2 scores was .22 indicating a relatively low, but statistically significant, correlation between fluid intelligence and mathematical abilities. The multiple regression analysis for the sample ( N = 109) yielded a Mult R value of .25 ( p < .05) between mathematical abilities and the predictor variables, indicating a relatively low, but statistically significant Mult R value between fluid and spatial intelligences and mathematical abilities, and with an R² of .062 indicating a small effect size. The stepwise regression analysis for the sample (N=109) yielded a Mult R value of .22 (p < .05), indicating a low relatively, but statistically significant, Mult R value for the stepwise regression, and with an R² value of .047 indicating a small effect size; which nonetheless indicated that fluid intelligence is a better predictor than spatial intelligence of mathematical abilities. Cross validation was used to validate the findings of both the multiple and stepwise regressions. Discussion of the results, further recommendations for research, and conclusion were also presented.