A new electrochemical sensor based on CdSe quantum dots-multiwalled carbon nanotube composite film (CdSeQDs-cMWCNTs) was developed for highly selective simultaneous determination of 1,4-dihydroxybenzene (hydroquinone, HQ) and 1,2-dihydroxybenzene (catechol, CC) in 0.1 M phosphate buffer solution (pH 7.4). CdSeQDs-cMWCNTs/GCE exhibited two well-distinguished anodic peaks with large currents for simultaneous detection of HQ and CC in comparison with bare GCE and cMWCNTs/GCE. Furthermore, CdSeQDs-cMWCNTs/GCE has an excellent anti-interference ability for the detection of HQ and CC in the presence of some inorganic compounds and phenol derivatives. Under the optimized condition, CdSeQDs-cMWCNTs/GCE showed wide linear responses from 0.5~\mu \text{M} to 110~\mu \text{M} for HQ, and from 0.5~\mu \text{M} to 110~\mu \text{M} for CC, with the detection limits of 0.35~\mu \text{M} and 0.25~\mu \text{M} , respectively. CdSeQDs-cMWCNTs/GCE was successfully applied to the simultaneous determination of HQ and CC in tap water with satisfactory recovery.