Digitalis trojana Ivan, a member of Digitalis genus, has highly bioactive properties due to, efficient phenolics. These compounds have shown to convert into each other in a limited time. Seasonal fluctuations of this plant leaves have been studied during the summer season using the high performance liquid chromatography-tandem mass spectrometry. Caffeic acid in June (2.48 mg/g extract), p-coumaric acid in August (6.69 mg/g extract) and trans-ferulic acid in July (4.85 mg/g extract) were the main compounds in the non-hydrolysed extracts. These compounds were heavily found in the hydrolysed extracts in August (14.63, 18.29 and 5.70 mg/g extracts, respectively). In addition, analysed flavonoids were found to be highest in July. Total phenolic contents were measured spectrophotometrically by using Folin-Ciocalteu's phenol reagent. The spectrophotometrically results were lowest (e.g. 43.50 mg GAE/g extract) in July while those of the hydrolysed extracts were highest (e.g. 167.19 mg GAE/g extract) in June. (C) 2016 Elsevier B.V. All rights reserved.