Abstract: In the study, a homolous gene encoding RIN4 protein was cloned from Populus euphratica. To clarify the role of PeRIN4 in salinity stress, PeRIN4 was introduced to Arabidopsis thaliana and plant response to NaCl was examined in transgenic plants. Salt-resistant phenotypes, activity of plasma membrane (PM) H⁺-ATPase and flux profiles of H⁺, Na⁺, K⁺ were screened in this work. Subcellular localization of PeRIN4 was determined by transforming the fusion protein of pGreen0029-PeRIN4-GFP into arabidopsis mesophyll protoplast. Results showed that PeRIN4 was localized in the cytoplasm. Seven-day-old seedlings of wild-type (WT), vector control (VC) and PeRIN4-transgenic arabidopsis were exposed to 100 mmol/L NaCl saline. PeRIN4-transgenic lines showed higher survival rates and root length than WT and VC plants. These results indicated that over-expression of PeRIN4 improved salt tolerance in arabidopsis. In addition, PeRIN4-transgenic arabidopsis exhibited a greater hydrolytic activity of PM H⁺-ATPase compared with WT and VC. Moreover, PeRIN4-transgenic roots showed a higher H⁺ and Na⁺ efflux than WT and VC, but displayed a less K⁺ loss under salinity conditions. We concluded that PeRIN4 could improve the activity of PM H⁺-ATPase under salinity environment. Under NaCl stress, the activated PM H⁺-ATPase could sustain an H⁺ gradient to drive the Na⁺/H⁺ antiport across the PM, thus enhancing Na⁺ exclusion, and preserve a less-depolarized membrane potential, thus restricting the K⁺ efflux through depolarization-activated outward rectifying K⁺ channels and non-selective cation channels. Our data demonstrate that PeRIN4 may improve salt adaptation in transgenic arabidopsis through controlling K⁺/Na⁺ homeostasis under salinity environment.