The natural bilayer fabric of ridge gourd vegetable belonging to the Cucurbitaceae family is treated with 2% aqueous NaOH solution. The primary thermograms of the fibers from this natural fabric of both the layers (top and bottom) before and after alkali treatment are recorded in an inert atmosphere at a heating rate of 10C/min. Using these thermograms, the initial and final degradation temperatures and inflection points are found. Employing the Doyle method, the integral procedural degradation temperature is also determined. The thermal stability of fabric for both layers is found to increase on alkali treatment.