This study was aimed at determining the nutrient composition and in vitro ruminal digestion values of Plantago lanceolata herbage in different phenological stages. The plant samples were gathered in the vegetative, flowering and early seed stages of the plant. The crude protein, diethyl ether extract, ash, non-fibre carbohydrates, and proanthocyanidins levels of the vegetative and flowering stages were higher than those of the early seed stage (P < 0.001). Structural carbohydrate levels (P < 0.05) were determined to have a higher value in the early seed stage. Glucose, fructose, Ca, K, Mg, P, Fe and Cu concentrations decreased as the plant matured (P < 0.001), but Na, Zn, and Mn concentrations increased (P < 0.05). The asymptote gas production, gas production rate (P < 0.001), total gas production at 24 h (P = 0.002), metabolic energy, net energy lactation and organic matter digestibility values and the number of Entodinium (P < 0.001) and total bacteria count (P = 0.026) of the flowering and vegetative stages were higher than those of the early seed stage. Methane produced by 0.2 g dry matter was similar in the three phenological stages (P = 0.078). The bound condensed tannins and saponin contents of plants and ammoniacal-N, number of total protozoa and pH value of rumen fluid were similar in the three different phenological stages (P > 0.05). The present study indicates that P. lanceolata in the vegetative and flowering stages has, owing to its chemical composition, energy content and digestibility, the potential to be used as a forage source for ruminants in areas affected by drought.