Malaysia is in the process of changing the medium of instruction for mathematics and science from Malay to English since 2003. To ensure the success of this transition, teachers have to be professional prepared to teach in English. This research aimed to survey the Malaysian science/ mathematics teachers’ perception towards this professional preparation effort. An instrument called “Teachers Perception Towards the Professional Preparation to Teach Mathematics/Science in English” was developed. The samples were 72 Form One mathematics/science teachers in Malaysia. The research revealed that the teachers perceived that their pre-service training (M = 2.90, SD = .57) and the in-service training (M = 2.99, SD = .62) is adequate in their professional preparation. However, the teachers perceived that there is a need (M = 3.18, SD = .82) for enhancing their professional readiness to teach mathematics/science in English. Further analysis revealed that 44.3 % of the sample reported that their pre-service training could not develop their confidence in English speaking and after the in-service training 31.4% of the teachers still reported the same. About 84.7 % of the teachers also reported the need for training on helping students to learn in English. The findings showed that although the teachers perceived they are professionally prepared to teach mathematics/science in English, they still need more preparation in overcoming students’ difficulties in learning the subjects in English especially for students who are weak in English or mathematics/science or both.