The initial adsorption process of Bi onto the Si(111)7×7 surface, including nanocluster formation, has been investigated by a real time structural analysis using in-situ RHEED intensity monitoring during the Bi adsorption, as a complementary approach to local and statistical structure analysis by STM. At an elevated temperature, the intensity distribution of 7×7 diffraction pattern varied gradually with the Bi adsorption and temporal intensity maxima which indicate the change of ad-layer symmetry without any serious disorder were observed. Subsequent STM observations clearly showed the formation of adsorption structure. From these results, multistep ordering process in Bi initial adsorption onto Si(111)7×7 was concluded, i.e. there are several coverage-dependent adsorption structures. Bi magic nanocluster was clearly observed by STM in atomic resolution. [DOI: 10.1380/ejssnt.2008.291]