Dyeing of polyester/cotton blends is usually carried out through the two-bath or one-bath two-step dyeing method using proper disperse dyes and reactive dyes for each fiber. However, the dyeing requires relatively long and complicated procedure as well as there are some problems such as lower dyeability. In the present study, new one-bath one-step dyeing process was investigated using disperse dyes having amino groups and hetero-bifunctional bridge compound(DBDCBS) including dichloro-s-triazinyl groups and ${alpha},{eta}$-dibromopropionylamido groups to improve the dyeability of cotton component in polyester/cotton blends. And the one-bath dyeing properties of polyester/cotton blends was evaluated by various dyeing conditions such as pH, temperature and dye concentration, The optimum dyeing condition was pH 4 and $110-120^{circ}C$. Color fastness were relatively good because of the colvalent bond formation between DBDCBS-reacted cotton fiber and disperse dye.