Guar esters of long-chain aliphatic carboxylic acids (fatty acid) were prepared and examined. Esterification was done in two steps, with the first goal to prepare acid chloride by refluxing acid with slight excess of thionyl chloride, and the product was confirmed by elemental analysis. Ten different types of fatty acid (C₅-C₁₈) were used for derivatization. The reaction mechanism for synthesis of fatty acid ester of guar was studied in detail. Physical properties of the esters were examined as well. The degree of substitution was calculated by titration method and structure elucidation was done using Fourier transform infrared spectroscopy (FTIR), proton-nuclear magnetic resonance (¹H-NMR) and scanning electron microscopy (SEM) techniques.