Silicon carbide (SiC) single crystal growth was studied by the in-situ observation using x-ray topographic technique. Occurrence and dynamics of defects, dislocations were observed in a real time display and captured as topographic images during sublimation growth (modified Lely method) of SiC crystals. From the analysis of these topographic images, high-density of dislocations and typical large defects, such as micropipes, domain boundaries and macrodefects were investigated. On the basis of our in-situ observation and analysis, we argue that dislocation and nucleation control on the seed crystal during initial growth are of prime importance for producing high quality SiC crystals.