This diploma thesis is concerned with the characterization of complex nonmetallic inclusions in ferroniobium, wich is cede to alloy steels. When niobium containing steels are cast by continuous casting machines, voestalpine Linz could observe the problem of clogging. This thesis deals with the identification and analysis of non-metallic inclusions in ferroniobium which end up in the ferroniobium during the production process. To characterize the inclusions methods like X-ray fluorescence analysis, scanning electron microscopy and the microprobe where used. Another aspect of this work was the development of an evaluation method for the automatic SEM/EDX-analysis. The investigations had shown a frequently appearance of alumina and titanium oxide, but no occurrence of niobium or ferrous oxides. The results of a quantitative analysis indicate that the non-metallic inclusions contribute only to a small extent to the problem of clogging in continuous casting machines.