The association constants (K) of 3,5,N-trimethyl pyridinium iodide in 95 volume percent ethanol-water mixed solvent were determined by a modified UV and conductance method at $25^{circ},;30{circ},;40{circ};and;50{circ}C$ over the pressure range 1 to 2000 bars. The association process is enhanced with increasing pressure and decreasing temperature. From K values, we obtained the total partial molar volume change (${Delta}V$) and some thermodynamic parameters. The electrostriction volume (${Delta}V_{el}$) and intrinsic volume (${Delta}V_{in}$) were also evaluated. The values of ${Delta}V,;{Delta}V_{el},;{Delta}V_{in}$ are negative, negative and positive, respectively, and the absolute values of all these three decrease with increasing pressure and temperature. The ion-pair size (a) were varied 3 to 6 ${AA}$<TEX>, with pressure and temperature. The solvation number (n) decreased from 2 to 0.5 with increasing temperature.