Capillary isotachophoresis (ITP) in cationic regime of the separation with conductometric detection has been used for the separation and determination of promethazine hydrochloride (PRO) in commercial mass-produced pharmaceutical preparations. Several electrolyte systems of different compositions and pH were examined and the optimized ITP electrolyte system consisted of 10 mmol/l of potassium acetate adjusted to pH 4.8 with acetic acid as the leading electrolyte with electroosmotic flow (EOF) suppressing additive, 0.2% (w/v) methylhydroxyethylcellulose (m-HEC), and 5 mmol/l of beta-alanine as the terminating electrolyte. The proposed electrophoretic method was successfully validated. It was convenient for the sensitive, simple, rapid, and highly reproducible assay of promethazine. The calibration graph relating the ITP zone length to concentration of the analyte was rectilinear in the range of 40-200 mg/l of the drug standard, with a coefficient of determination r(2)=0.9992. The relative standard deviation (RSD) was 1.12% (n=6) when determining 100 mg/l of PRO in standard sample. Good quantitation was obtained in short analysis time (a single analysis took 6 min). The recoveries of drug from samples were found to be 97.22% (tablets), 99.72% (injections), and 99.14% (syrup). The minimal sample pretreatment and low running cost make the proposed ITP method a good alternative to commonly used analytical methods.