Abstract:Three monocotyledenous halophyte seedlings (Puccinellia tenuifiora (Griseb.) Scribn. Merr., Aneurolepidium chinese (Trim.) Kitag. and Aeluropus sinensis (Debeaux) Tzvel. ) were treated with different concentration, of NaC1 for two weeks. Their growth status, the contents of main organic solutes and inorganic ions, the osmotic potential and osmotic adjustment ability were then determined. The results are as follows: Of all the inorganic osmotica, the contents of Na + and C1－ increase with salinity, while K + decreases. The other ions such as Mg7 + , Ca2 + and NO3－either increase or decrease with salinity. Overall, the contribution of ions to osmotic adjustment decreases with salinity, and Na+ and Cl－ play the most important role. As for the organic osmofica, however, they all increase with salinity except for organic acid, and the most increased is soluble sugar, of which sucrose is important, which is 1/2 of the soluble sugar. Further more, the Na+/K+ ratio of the 3 plants is about 1 except for A. sinensis, whose Na+/K+ ratio is bigger under high salinity. On the other hand, the measured osmotic potential (MOP) is bigger than computational osmotic potential (COP), which implies that there still exists other osmotic in the plants except for the 11 substances determined in the experiment. The paper explains the reasons for all the above results.