Vernonanthura tweedieana (Baker) H. Rob., Asteraceae, is used in the Brazilian folk medicine for the treatment of respiratory diseases. In this work the phytochemical investigation of its ethanol extracts as well as the development and validation of an UPLC-PDA method for the quantification of the eriodictyol from the leaves were performed. The phytochemical study for this species lead to the identification of ethyl caffeate, naringenin and chrysoeriol in mixture, eriodictyol from leaves, and the mixture of 3-hydroxy-1-(4-hydroxy-3,5-dimethoxyphenyl)-propan-1-one and evofolin B, apigenin, the mixture of caffeic and protocatechuic acid and luteolin from stems with roots, being reported for the first time for V. tweedieana, except for eriodictyol. The structural elucidation of all isolated compounds was achieved by 1H and 2D NMR spectroscopy, and in comparison with published data. An UPLC-PDA method for quantification of the eriodictyol in leaves of V. tweedieana was developed and validated for specificity, linearity, precision (repeatability and intermediate precision), limit of detection (LOD) and limit of quantification (LOQ), accuracy and robustness. In this study, an excellent linearity was obtained (r2 = 0.9999), good precision (repeatability RSD = 2% and intermediate precision RSD = 8%) and accuracy (average recovery from 98.6% to 99.7%). The content of eriodictyol in the extract of leaves of V. tweedieana was 41.40 ± 0.13 mg/g. Thus, this study allowed the optimization of a simple, fast and validated UPLC-PDA method which can be used to support the quality assessment of this herbal material.