The objective of this study was to identify the reasons for shortage of Mathematics teachers at Thai Basic Education level. This research is both quantitative and qualitative in nature. For the purpose of study, survey was conducted with senior high school students, in order to find out their willingness to pursue mathematics in Bachelor of Education. Further, in-depth interviews was conducted with Teachers' Council personnel, The Institute for the Promotion of Teaching Science and Technology, Office of the Basic Education and other persons' who are in the position of Dean or Deputy Dean of higher educational institutions from both governmental and private institutions that have B.Ed. Mathematics programme. The sample was chosen from 4 regions of Thailand and it has been contributed to 400 samples. The descriptive statistics is used to identify the frequency. Based on the qualitative results, it is found that the shortage of mathematics teachers exists at both primary and secondary level. Further, substitutions were not made for retirements, and capable people were moved to administrative jobs; also those who work in both primary and secondary schools were not from mathematics background. Quantitative results revealed that the only 12.2% of the students are interested to pursue faculty of education, in that only 6.1% are willing to choose mathematics in bachelor of education. Majority of the students are interested to teach general science subjects after their graduation; and willing to teach in normal classes. And most of the students are willing to teach in Thai, after their graduation. The reasons behind the shortage of mathematics teachers are only few students' show interest to study mathematics due to the difficulty in mathematics, lack of good mathematicians, low pay, etc., hence proper motivation and guidance should be given to students. Finally, the guidelines were suggested based on in-depth interviews for producing mathematics teachers in 21st century. Conclusion and recommendations are presented for further study to address this issue.