The present study was conducted to explore the floristic composition, life form, and leaf size spectrum of vegetation, seasonality, and habitat condition of the Sultan Khail valley, Hindu Kush range, Pakistan. Regular trips were arranged during 2017–2019 to collect plant specimens and prepare a checklist of the flora of the area. The life form and leaf size spectrum of vegetation were determined. The plant species were also classified based on their habitat. The area is home to 332 species belonging to 234 genera and 96 families. Asteraceae (32 species) was the dominant family in the area, followed by Rosaceae (28 species) and Lamiaceae (21 species). Therophytes were found to be dominant in the area, followed by phanerophytes, while microphylls were the dominant leaf size class, followed by nanophylls. Seasonal variation in life forms showed that the spring, autumn, and winter seasons' flora was dominated by phanerophytes, while therophytes were dominant in the summer season. Seasonal variation in leaf size spectra showed that microphylls were dominant in the spring and summer, while in the autumn and winter seasons, nanophylls were dominant. The highest numbers of species were found in dry places, followed by forests. The flora of the study area is diverse. The habitat condition of the area is dry. The area's phytoclimate is thero-phanerophytic. The flora of the area is subjected to severe anthropogenic stress and needs proper conservation.