Abstract: The paper reports the results using Caesium-137 technique to investigate soil erosion rates and sediment sources and its changing of Zhaojia gully catchment in the rolling Loess Plateau re-gion of Zhichang County, Shaanxi province, China, where absence of direct measurements of the soils erosion rates and sediment source observation, the results of the paper derived from reservoir deposited and from Caesium-137 measurement.Soil samples were mainly collected from the cultivated slope land in the loess hills, steep gully area and the sediment deposited in sediment trap reservoirs, and the Caesium-137 refer-ence samples collected from a plain grassland, where no disturbance sine 1953,and same altitude as the study cultivated slope land.The references inventory of Caesium-137 in study region was 2 504 Bq/m², and the average Caesium-137 content of the rolling cultivated slope land and the steep cultivated slope land were 1 248- 2 Bq/m² and 443. 1 Bq/m² respectively. Based on measurement of the Caesium-137 con-tent of these soil samples, the estimated net erosion rates on cultivated land occupying the gen-tle crest slopes and steeper lower slopes of the rolling plateau and the steep gully slopes were 4 158 t/km²?a, 8 584 t/km²?a and 15 851 t/km² ?a, respectively, and the rolling cultivated slope land and steep gully slope land were 6 580 t/km² ?a and 21 118 t/km² ?a respectivelyThe average content of surface samples collected from the rolling cultivated slope land, and the steep gully area were 3. 88 Bq/kq and 0. 02 Bq/kg respectively. The average content of thesediments deposited in dam 3 was 0. 91 Bq/kg. According to analysis of the Caesium-137 content of surface soil samples from the rolling cultivated slope land and gully slope land and the sedi-ment deposited in sediment trap reservoirs, the relative contribution of sediment from the rolling Plateau and gully area were estimated to be 24％ and 76％ respectively. Analysis of the sedi-ment deposited dating from 1973～977 in another sediment trap reservoir enable individual flood event couplets to be identified and indicated that the sediment associated with the first one or two floods in a season, when the soils of the plateau area were relatively dry, the sediment of the reservoir was derived primary from the gully areas, the cultivated soils of the rolling plateau contributed an increased proportion of the total sediment yield during the latter stages of the flood season when the soils were wetter and surface runoff and erosion were more widespread.

Key words: sediment sources, Caesium-137 technique