Abstract: The ontogeny of chloroplast in satsuma mandarin (Citrus unshiu Marc. cv. Okitsu Wase) young leaves sprayed with urea was studied under transmission electron microscope. Leaves at 20 days after budding (DAB) exhibited undifferentiated mesophyll cells containing chloroplasts at different developmental stages for both control and urea-applied trees. However, in urea-applied trees the chloroplasts at different developmental stages were usually smaller and devoid of starch grains. Both control and urea-applied trees had almost similar pattern of chloroplast development which yielded six stages and are described in this paper.