Pressure assisted capillary electrophoresis was applied to determination of acid dissociation constants (pK a ) of six widely used triazole fungicides (cyproconazole, epoxiconazole, flusilazole, tebuconazole, penconazole and propiconazole) in aqueous medium. The pK a values were determined from the dependence of effective electrophoretic mobility of the triazole fungicides on p[H + ] of the background electrolyte (BGE) using non-linear regression analysis. The p[H + ] was used instead of pH to reflect the increased ionic strength of the strongly acidic BGEs (pH<1.75) as compared to the BGEs at pH equal to or greater than 1.75. Prior to the pK a calculation, the measured effective electrophoretic mobilities were corrected to the reference temperature (25°C) and constant ionic strength (25mM). The regression function was modified to allow the determination of pK a in the BGEs of varying ionic strength. The electrophoretic measurements showed that the above triazole fungicides are very weak bases – their pK a values were found to be in the range 1.05–1.97 and were in a good agreement with the values calculated by SPARC online pK a calculator.