Cassia ferruginea (Schrad.) DC. (Fabaceae) is a native plant widely used as an ornamental tree and for the restoration of degraded areas in Brazil. Although no previous ethnopharmacological or chemical information was available, bioprospecting studies on this species found out a high concentration of dihydromyricetin (DHM) in different parts of the plant. DHM, also known as (+)-ampelopsin, is a flavonoid that presents important pharmacological and biological activities, including anticancer, cardioprotective and hepatoprotective effects. The aim of this study was to develop and validate a simple method for the determination of DHM in hydroethanolic extracts of C. ferruginea by quantitative 1 H NMR (qHNMR) using the internal standard approach. The parameters as linearity, specificity and selectivity, accuracy, precision (repeatability and intermediate) and robustness showed satisfactory results. Five ethanolic extracts from different stages and organs of C. ferruginea were investigated, the DHM concentration ranges from 52.08 ± 3.95 to 201.83 ± 4.71 mg/g. The proposed method appears to be a suitable tool for fast quality control of herbal extracts, with no need of tedious sample preparation and chromatographic separations increasing the efficiency of natural products analysis. This is the first study reporting the presence and determination of DHM in Cassia ferruginea (Schrad.) DC.