In this first part of a two part series, the pore structure of zirconia-silica composite stationary phase supports was examined using size exclusion chromatography. The study found that the pore structure was more complex than pure zirconia surfaces. With these composite materials, the pore dimensions are primarily dependent on the concentration of the silicon doping, the temperature of calcination, and the presence of salts during calcination. Silicon concentration influences the phase crystallization which, in turn, alters the temperature at which micropores transform to mesopores. Calcination in the presence of sodium chloride increased the surface area and pore volume of the support.