Lemon balm is a perennial herb. The stems are erect or nearly erect, much-branched, with most branches spreading in a pyramidal shape from the middle or lower part of the stem. They are quadrangular with four shallow grooves, covered in soft hairs, becoming gradually glabrous towards the base. The leaves are petiolate; the petioles are slender, 0.5–2 (4) cm long, covered with long soft hairs. The leaf blades are ovate, generally up to 5 (6.5) cm long and 3–4 (5) cm wide on the stem, smaller on the branches, 1–3 cm long and 0.8–2 cm wide. The apex is acute or obtuse, the base is rounded to nearly cordate, rarely obtuse or acute, with serrate-crenate or bluntly serrate margins. The texture is nearly membranous or herbaceous. The upper surface is covered with long soft hairs, while the lower surface is only hairy along the veins. There are 4 pairs of lateral veins, which are flat on the upper surface and raised on the lower surface, with the reticulate veins conspicuous above. The verticillasters are axillary, with short peduncles, bearing 2–14 flowers. The bracts are leaf-like, much smaller than the leaves, covered with long soft hairs and ciliate margins. The flower pedicels are about 4 mm long, covered with long soft hairs. The calyx is bell-shaped, about 8 mm long, externally covered with jointed long soft hairs, internally hairy above the middle, bilabiate. The upper lip is broad, with 3 very short teeth or nearly shallowly undulate, the tooth tips with short points. The lower lip is slightly longer than the upper lip, 2-toothed, the teeth long triangular with long spinose tips. The corolla is creamy white, 12–13 mm long, covered with soft hairs; the limb is bilabiate, the upper lip straight, slightly notched at the apex, the lower lip 3-lobed, the middle lobe largest, spreading obliquely, rounded at the apex. There are 4 stamens, included or nearly exserted. The style is equally 2-lobed at the apex. The disk is shallowly 4-lobed, the lobes alternate with the ovary lobes. The nutlets are ovate. The flowering period is from June to August.