Three seed lots of cucumber (Cucumis sativus L.), cv. Rubi, were germinated in blotter paper soaked with solutions of NaCl. The effect of water stress during seed germination and development of cucumber seedlings was evaluated by submmiting seeds to five osmotic potentials (0.0; -0.2; -0.4; -0.6 and -0.8MPa). Research was conducted at the Seed Analysis Laboratory of the Department of Crop Science of the College of Agriculture ?Luiz de Queiroz?(USP/ESALQ) from March to May 1999. Percentage of germination, first count, abnormal seedlings, seedling length and dry matter weight production of seedlings were evaluated. Results showed that the gradual reduction of the osmotic potential of substrate caused a reduction of germination and of development of cucumber seedlings; osmotic potentials lower than -0.4MPa were considered as critical.