Abstract:Water uptake of tomato (Lycopersicon esculentum Mill. cv. Moneymaker) seeds during germination was obviously triphasic. The completion of the first phase of water uptake by whole seed could not be realized until 10～12 h later after sowing though varies in different parts of seed. The mechanical resistance of endosperm and seed coat restricted water uptake of the embryo envoleped by the endosperm. Water potential of the intact embryo was still 0. 6～0. 9 Mpa lower than the whole seed when the equilibrium between seed and imbibing solution was established. GA and ABA had no direct effects on the water uptake of tomato seeds. The water potential of embryo was positively correlated with its moisture content. The osmotic potential of tomato embryos decreased slowly during imbibition in water and osmotic solution as well.