Backround: This study was carried out to determine the nutritional value and methane production potential of Phacelia tanacetifolia plant in different growth stages in April-May year in the ecological conditions of the province of Adiyaman in Turkey. Methods: Phacelia (Phacelia tanacetifolia) plant samples were collected with four replications in four different stages, pre-flowering, early flowering, mid-flowering and end of flowering (seeding). The nutrients of the feed samples were determined. The gas production was measured after 24 hours of incubation of the forage with rumen fluid. Result: The effect of harvest time on chemical composition was highly significant. In vitro gas production was lowest in stage I. and highest in II. The methane (CH4) lowest production values were found in the 1st stage, whereas the highest value was observed in the 4th stage (seed-binding stage), where the difference was statistically significant. ME was 7.49, 9.54, 8.90 and 8.61 MJ/kg DM respectively and the difference between the stages was statistically significant. It was concluded that Phacelia tanacetifolia, which is known as an important nectar source in the world and in Turkey. It is appropriate to harvest the phacelia plants in the second stage, i.e., at early flowering for higher ME contents and OMD.