The aim of this paper was to examine the determinants of over education and under education in the formal labour market of Tanzania. The study employed cross sectional and worker self-assessment (WSA) techniques. Interviews were conducted to collect data from 319 employees. Using multinomial logit model analysis, the results revealed that workers in the formal sector with age between 29 and 50 years and who had access to transport were likely to be over educated. On the basis of location, workers in urban and rural areas were likely to be over educated and under educated respectively. Therefore, Tanzania labour market is not free from over education and under education problems and their negative effects on wage, job satisfaction and service delivery can not be ignored. It is therefore recommended that private and public sectors should harmonise standards of recruitment and motivation to mitigate incidences of over education and under education.