With a renewed interest in soil quality and long-term sustainability, the Soil Organic Carbon (SOC) status has taken on new significance today. Were evaluated the long-term fertilization and rainfall effects on SOC changes of a Haplic Luvisol in a long term field experiment with ray, potato, winter wheat and triticale indicator plants in a fragile agro-ecological circumstances at Nyírlugos (Eastern Hungary) from 1962. to 2002. The soil had the following agrochemical characteristics: pH (H2O) 5.9, pH (KCl) 4.7, hydrolytic acidity 8.4, hy1 0.3, humus 0.7%, total N 34 mg . kg-1, ammonlactate (AL) soluble-P2O5 43 mg . kg-1, AL-K2O 60 mg . kg-1 in the plowed layer. From 1962 to 1980 the experiment consisted of 2x16x4x4=512 plots and from 1980 of 32x4=128 plots in split-split-plot and factorial random block designs. The average fertilizer rates in kg . ha-1 . year-1 N 45, P2O5 24, K2O 40, MgO 7.5 until 1980 and N 75, P2O5 90, K2O 90, CaCO3 437.5, MgCO3 140 kg . ha-1 . year-1 after 1980. In 1963, 1973, 1983, 1988, 1998 and 2002 soil samples had been collected (0- to 20-cm depth consisting of 20 sub-samples) from the field treatments. SOC content measured by dichromate oxidation using the HR-080452-80 protocoll by Baranyai 1987. Precipitation datas had been harvested in Meteorological Station at Napkor. The main results and conclusions are as follows: In F plots, the SOC pool significantly (P( 0.05) decreased (F0, -10.3%( N, -31.0%( NP, -12.1%( NK, -13.8%( NPK, -12.1%( NPKCa, -13.8%( NPKMg, -22.4 %( NPKCaMg, -13.8%) from 1963 to 1982. Conversely, after 20-yr (from 1983 to 2002) the SOC sequestration increased (F0, 7.7%( N, 70.0%( NP, 37.3%( NK, 38.0( NPK, 39.2%( NPKCa, 30.0%( NPKMg, 62.2%( NPKCaMg, 30.0%). On average of 40-yr, at pure F0 plots, the SOC concentration remained nearly constant. Fertilization in comparison with F0 significantly (P( 0.05) increased SOC (N, 3.2%( NP, 11.4%( NK, 7.0%( NPK, 14.0%( NPKCa, 6.4%( NPKMg, 6.4%( NPKCaMg, 5.2%). SOC stores in soils decreased linearly by increasing rainfall (477 to 572 mm . yr-1).