Recent years have witnessed less attention paid on soil acidification in the red soil region of Southern China, though it remains to be one of the main problems in the red soil ecosystem. So it is of great significance to explore temporal-spatial variability of soil pH in designing reasonable measures for agriculture and environmental management in the region. Analysis was done of the data of soil sampling in Yujiang in 1982 and 2007 for spatio-temporal distribution and variation of soil pH in the region during the two sampling periods and trend of the variation in the past 25 years. Results showed that the soil pH in Yujiang County has been obviously declining since the 2nd National Soil Survey. It declined from 5.66 in 1982 to 4.74 in 2007. Among the main types of soils that Yujiang has, fluvo-aquic soil dropped the most or by 1.02 in soil pH, and was followed quite closely by paddy soil and red soil, which did by 0.89 and 0.88 respectively. Among the main land use patterns, paddy field and upland field declined by 1.00, 0.92 and 0.82, respectively. Among the regions of the county, most declined sharply, especially parts in the central-northern and southwestern regions, which accounted for 68.13% and 84.54% of the total land area of Yujiang County, respectively. Compared with 1982, 2007 saw soil pH in the two parts dropping by 0.4~0.8 and 0.8~1.2, separately. Furthermore, the county was dominated by weakly-acid soil in 1982, while about 13.0% of the county’s soil turned to be strongly-acid in 2007, with the remaining being nearly the same, that is, strongly-acid. All the findings in this study indicate that the soil in Yujiang county, regardless of soil types and land use patterns, declined in pH by a large margin in the 25 years from 1982 to 2007. So the situation of soil acidification is very serious in the county, calling urgently for effective remediation measures.