Fe-based metallic-glass (MG) ribbons have attractive soft-magnetic properties for energy applications. Nevertheless, these MG ribbons produced by industrial processes suffer from surface crystallization on melt-spun ribbons, which causes a significant damage of their magnetic properties. In this study, the surface crystallization behavior has been carefully analyzed by various micro-analytical tools. It is surprisingly to find out that such surface crystallization involves two critical steps. First, some active impurities diffuse to ribbon surface and result in the formation of oxide particles. Second, these oxide particles trigger a massive formation of Fe-rich nanocrystals around these oxides. The understanding of the formation mechanism leads to ways to solve the critical production problem. The research is supported by the Hong Kong GRF under the contract No. CityU 102013 and the NSFC China contract No. 51601206. Paper to be presented at TMS 2018 Annual Meeting to be held on March 11-15, 2018 in Phoenix, Arizona.