In this study, we investigated the chemical composition and hygroscopicity of water-soluble fraction in PM2.5 collected from a rural site of Guanzhong Basin, a highly polluted region in northwest China. Hygroscopic growth factors, g(RH), of water-soluble matter(WSM) were measured by hygroscopic tandem differential mobility analyzer(H-TDMA) with an initial dry particle diameter of 100 nm. The g(90)WSM and κWSM was in the range of 1.08~1.49(1.35{plus minus}0.10) and 0.04~0.29(0.19{plus minus}0.06) in summer, 1.24~1.45(1.36{plus minus}0.07) and 0.12~0.26(0.20{plus minus}0.04) in winter, respectively. We found that increased nitrate concentration at night in summer suppressed 60-70% of the deliquescent point, and increased g(RH) at elevated relative humidity, compared to daytime. Secondary inorganic ions were the main components in heavy haze day, and greatly contributed to the hygroscopicity of particles. In contrast, more potassium compound and WSOM existed during Chinese Spring Festival event but exhibited no deliquescence point in the process of hygroscopic growth with the elevated RH. The g(90)WSOM and κWSOM, obtained using ZSR model, were in the range of 1.06~1.52(1.25{plus minus}0.14) and 0.024~0.32(0.13{plus minus}0.09) in summer, 1.06~1.58(1.38{plus minus}0.15) and 0.02~0.38(0.22{plus minus}0.10) in winter, respectively. The mean g(90)WSOM was in the range of that of biomass burning aerosols, and a good correlation (R=0.71) was found between g(90)WSOM and levoglucosan, confirming that the aerosol’s hygroscopicity were highly influenced by biomass burning in winter. Briefly, it is revealed that the aerosol in rural regions of Guanzhong Basin is mainly influenced by biomass burning based on the hygroscopicity in winter and summer.