Lagerstroemia langkawiensis is being described as a small to medium-sized tree that can grow up to 5-16 m tall with bole measuring around 12 cm in diameter. It has a smooth texture and creamy pale brown bark with thin scales flake. It has a lanceolate leaf with glabrous lamina, rounded base, acute apex and petiole around 0.5 cm long. The inflorescence arises from the end of a stem along with bright pink flowers that turn white with age. The longer filaments of the flowers are purple with blackish anthers while shorter filaments are whitish or pale pink with yellow anthers. It has 15-18 mm long blackish capsules with smooth or indistinctly wrinkled that are covered with hair mainly at the apex (de Wilde, Duyfjes & Siti-Munirah, 2021).

This species is mostly known from Perlis and Kedah, on Langkawi Island and the mainland. It can be found in areas such as limestone, quartzite and shale, at sea level on the beaches or at low altitudes.