General cognitive and specific numerical abilities that underlay mathematical performance have been heavily investigated among hearing students; however, the inquiry has rarely been applied to students who are deaf or hard-of-hearing (d/Dhh). We examined whether general cognitive abilities (i.e. nonverbal IQ, processing speed, and spatial ability) and specific numerical abilities (i.e. symbolic and non-symbolic numerical magnitude processing) are related to mathematics achievement in 198 d/Dhh students in Grades 3 to 9. The results of our regression models indicated that, the three general cognitive abilities independently explained the variance in mathematics achievement when entered in one step; and spatial ability and processing speed had an independent contribution to mathematics achievement in the presence of the specific numerical abilities. The specific numerical abilities independently explained the variance in mathematics achievement when entered in one step; however, none of them had an independent contribution to mathematics achievement in the presence of the general cognitive abilities. These findings suggested that mathematics achievement in d/Dhh students depended more on general cognitive abilities, such as spatial ability and processing speed, than on specific numerical abilities.