Formic acid was reacted with different kinds of starch to yield O-Formate derivatives. Starches used included corn starch, rice starch, and oxidized corn starch. Thus obtained O-formates derivatives were submitted to assessment for acyl content, the degree of substitution (D.S), solubility and rheological characteristics. The highest%acyl and DS value were obtained with cornstarch and the least values with rice starch while oxidized corn starch stood in Mid-way position. All these starch formate derivatives displayed non-Newtonian thixotropy. Nevertheless, the degree of thixotropy and situation of the rheogram with respect to the rate of shear axis were determined by both natures of the starch before derivatization and storing the time of the paste. The degree of derivatization of starch via O-Formylation expressed as D.S., was a governing factor for the apparent viscosity of the pastes. Color strength (K/S) and fastness of cotton printed using the starch derivatives in question were very comparable, if not higher than those obtained with the conventional British gum thickener. This was observed irrespective of the D.S. of the formate derivatives of starch and time of printing paste storing and advocated current thickeners as good substitutes for conventional printing thickeners.