Fabrics obtained from natural fibres represent an important field of textile industry. The specific lignocellulosic/cellulosic structure gives special chemical, technological and thermal properties. The influence of different treatments applied on the fabrics could be determined using various analyses. All treatments and preparation methods applied on fabrics influence their thermal behaviour. Another important aspect which has significant influence is the heating rate [1]. The flax fibres are lignocellulosic type. To improve the flax fabrics quality those are subject of a pre-treatment to remove the impurities presented (wax, organic acids, pectin, salts). From economical and ecological point of view it is recommended the bioscouring treatment. This involves an enzymatic process for the pectin degradation [2]. Our study determined the influence of an ultrasonic reaction media on the efficiency of the pectin degradation process by using thermal analysis. It had been demonstrated that using ultrasound in textile industry improves the diffusion coefficient of the reaction compounds and also the fibres swelling in water [3]. For this, a comparative bioscouring treatment with and without ultrasound was made on 40% flax-60% cotton fabrics using two variables: enzyme concentration and treatment time. The reaction media consisted in an aliquot of commercial pectinolytic product called Beisol Pro, Denimcol Wash-RGN as detergent from CHT Bezema Company and a chelating agent (sodium citrate) in distillate water. All results obtained from different analyses such as: thermal analysis, IR, weight loss, hydrophilycity, whiteness degree, colorimetric analysis, tensile strength and elongation at break underline the positive effect of the ultrasound in the bioscouring process.