This paper examines the socio-economic determinants of age at first marriage of the ethnic tribal women of Bangladesh. Cox proportional hazard regression analysis was applied to the data set containing 792 observations from four different tribal communities compiled on the basis of a household survey. The singulate mean age at marriage (SMAM) of the women, and mean age at first marriage for females, were found to be 21.8 years and 18.9 years, respectively, which were much higher than those at the national level. Findings revealed that woman's educational attainment and pre-marital work status significantly delayed the timing of marriage. Parents’ economic status and respondents’ birth order had the most significant effect on marital timing. The multivariate statistical analyses also identified several variables as important determinants of marriage timing for the tribal women, including ethnic identity, childhood place of residence, father's literacy and father's survival status. The findings of the study may provide a clue to the rising age at first marriage of the disadvantaged indigenous women.