Students' attitude towards Mathematics seems to be an important factor essential for consideration in the teaching and learning of Mathematics. Hence, finding ways to improve students’ attitudes is imperative. To this end, this study investigated the effects of mother tongue as a supplementary medium of instruction on Secondary School Students’ attitude towards Mathematics in Ekiti State, Nigeria. The purpose was to examine the effectiveness of the mother tongue as a supplementary medium of instruction as it affects students' attitude towards Mathematics. The study adopted a quasi-experimental research design. The sample for the study consisted of 194 Junior Secondary School class one students selected from three secondary schools in Ekiti State through multistage sampling technique. A validated instrument tagged SAQM with a reliability coefficient of 0.85 was used for data collection. Results from the findings revealed a significant difference between the attitude of students exposed to mother tongue as a supplementary medium of instruction and those not so exposed. It was concluded that the use of the mother tongue as a supplementary medium of instruction is an effective tool through which students' attitude can be improved. It was recommended that teachers try as much as possible to incorporate the learners’ mother tongue during classroom interactions to enhance productivity in the learners.