The young first leaves (blade length, approximately 1.1 cm) of cucumber (Cucumis sativus L.) seedlings are covered by long and dense trichomes. Abscission of these long trichomes and growth of other new trichomes, a process referred to as molting of trichomes, occurs over the first 7 days of leaf development. We examined the effect of continuous ultraviolet-B (UV-B; 290-320 nm) irradiation on the development of the young first leaves of cucumber seedlings for 7 days. The first leaves of UV-B-irradiated cucumber seedlings at day 7 were shorter than those of the control seedlings. The density, length and cell number of trichomes on the surface of the first leaves of UV-B-irradiated cucumber seedlings at day 7 were greater than those in the control seedlings. We found that the initial long and dense trichomes do not abscise and other new trichomes grow on the surface of the first leaves of UV-B-irradiated cucumber seedlings for 7 days. Thus, continuous UV-B irradiation inhibits abscission of initial long trichomes, thereby maintaining the hairy surface of the young first leaves in cucumber seedlings.