Polyscias kavaiensis is a tree reaching heights of 8 to 25 meters. The foliage consists of compound leaves arranged alternately, with blades extending 25–90 cm in length. These blades support 11 to 21 leaflets, ranging from ovate to narrowly oblong shapes, typically folding upward along the midvein and measuring 7–20 cm in length and 3–89 cm in width, with the base pair appearing smaller. The leaflet apices vary from rounded to acuminate, while the bases range from rounded to truncate or cordate, often showing an oblique orientation. A distinctive feature is the dense scurfy stellate tomentose covering on the lower surfaces of the leaflets, especially pronounced in younger foliage. Margins are entirely smooth, and the leaflets are connected to the main blade via petiolules measuring 5–12 mm in length. Stipules are either absent or rudimentary, further detailing the leaf structure. Floral characteristics include racemose-umbellate inflorescences and stout primary and pendent secondary axes. Flowers, both bisexual and actinomorphic, emerge primarily at terminal umbellules, with a few situated laterally. Pedicels extend 3–8 mm long, elongating to 12 mm as fruits develop. The corolla is composed of 6–8(9) yellowish-green lanceolate petals. The partly inferior ovary supports 2–5 carpels, with sessile stigmas. The fruits are purple drupes, transitioning from globose to ovoid or cylindrical shapes, with a conspicuous calyx ring. Each fruit encapsulates a single seed within its pyrene. It occurs in mesic to wet forests between 650-1,600 meters.