Chitosan liquid fertilizer combined with ammoniumsulfate fertilizer (21-0-0) was not effect on growth of baby pak choi. It might be the effect of ammonium sulfate that added together with chitosan and control(only ammonium sulfate). Urea has the highest nitrogen content. It is the essentialelement for plant growth at vegetative stage(Vincent, 1964).Following Adisak(2008)reported that chitosan compound did not effect on plant height, number of leaves and yield of Pak choi. Therefore, this results suggested thatammonium sulfate or urea fertilizer was enough for vegetative growth of baby pak choi.