The relative viscosities ${eta}_r$ of a series of homologous tetraalkylammonium chlorides $Me_4NCl,;Et_4NCl,;Pr_4NCl;and;Bu_4NCl$ in a series of isopropanol-water mixtures have been determined at $30^{circ}C$ using Ubbelohde-type viscometers. The viscosity data have been interpreted in terms of viscosity A-and B-coefficients calculated from the Jones-Dole equation, ${eta}_r=1+AC^{1/2}+BC$. The results indicate that the structure-breaking effect of chloride ion is maximum at 0.l~0.15 mole fraction isopropanol, while the size effect(Einstein effect) of the larger $R_4N^+$ ions is maximum at 0.2~0.25 mole fraction. The results also indicate that in aqueous and water-rich solutions the larger $R_4N^+$ ions (e.g. $Pr_4N+, Bu_4N^+$) appear to be excellent structure-formers and that the viscosities of solutions is not strongly affected by the electrostriction effect of chloride ion.