Plant $Na^+/H^+$ antiporter plays a critical role in plant salt tolerance. In this study, AtNHX1, a vacuolar $Na^+/H^+$ antiporter from Arabidopsis thalina, was introduced into Petunia hybrida using Agrobacterium-mediated methods. Polymerase chain reaction (PCR) and DNA gel blot analysis confirmed that AtNHX1 was successfully integrated into the P. hybrida genomes. Reverse transcription (RT)-PCR analysis indicated that AtNHX1 expressed highly in transgenic plants. It was found that the 35S::AtNHX1 transgenic P. hybrida plants showed much more resistant to high concentrations of NaCl and to water deprivation than the isogenic wild-type (WT) Petunia plants. The transgenic plants accumulated more $Na^+$, $K^+$, and proline in their leaf tissue than that of the WT Petunia plants and maintained high water contents and high ratio of $K^+/Na^+$. These results demonstrated that over-expression of the vacuolar $Na^+/H^+$ antiporter conferred both salt tolerance and drought tolerance to the transgenic Petunia plants.