Erosion processes in all their forms (sheet erosion, rill erosion, gully erosion) are widespread in the territory of the Eastern Rhodopes, Bulgaria. They are conditioned by significant deforestation, the highly weathered Paleogene volcanics, and steep slopes. The aim of this study is to analyze geomorphological characteristics of gully erosion in the middle part of the river Mashkulova catchment and to characterize the deposits (petrographic composition, grain size, degree of weathering, sorting, etc.) in order to determine the conditions of transport and accumulation. The river Mashkulova is a small river that flows through the low mountains to the hilly relief of the Eastern Rhodopes Mountains (southern Bulgaria) and flows into the river Golema reka which confluences into the dam Kardzhali. For the purpose of the study, morphometric and sedimentological analyses of a slope with rill and gully erosion were carried out. The morphometric analysis was done on the base of a 12 m horizontal resolution digital elevation model. Sedimentological analyses give information about grain properties in the gully bed and on the slope. Monitoring of the temporal changes in grain size properties allows to characterize the dynamics of erosion and deposition, as well as the stages of development of the gully. The results of the field research show that the gully was incised into highly weathered migmatized biotite gneisses and amphibolite. Significant slope gradients (over 15°), the dominance of the sand fraction in all samples, and poor or very poor sorting are also observed. The obtained data provide information on the conditions of development of gully erosion and deposition in the watershed of the river Mashkulova and can be used for the assessment of erosion susceptibility, and for planning anti-erosion measures.