Bulk metallic glass formations in the Fe-B-Y-Nb quaternary alloy system were in-vestigated by using the cluster line rule in combination with the minor alloying principle. The Fe-B-Y ternary system was selected as the basic system and the intersections of cluster lines were taken as the basic ternary compositions. The basic compositions were further alloyed with minor amounts of Nb. After 3-5 at.% Nb was added,the basic composition Fe68.6B25.7Y5.7,which was developed from the most densely packed cluster Fe8B3,formed 3 mm bulk metallic glasses. These quaternary bulk metallic glasses (Fe68.6B25.7Y5.7)100-xNbx (x=3-5 at.%) are expressed approximately with a unified simple composition formula: (Fe8B3)1(Y,Nb)1. The (Fe68.6B25.7Y5.7)97Nb3 bulk metallic glass has the largest glass forming ability with the following characteristic parameters Tg=907 K,Tx=1006 K,Tg/Tl=0.644,γ=0.434,and longness t=22 mm. The combination of the cluster line rule and the minor-alloying principle is a promising new route towards the quantitative composition design of multi-component metallic glasses. Bulk metallic glass formations in the Fe-BY-Nb quaternary alloy system were in-vestigated by using the cluster line rule in combination with the minor alloying principle. The Fe-BY ternary system was selected as the basic system and the intersections of cluster lines The basic compositions were further alloyed with minor amounts of Nb. After 3-5 at.% Nb was added, the basic composition Fe68.6B25.7Y5.7, which was developed from the most densely packed These quaternary bulk metallic glasses (Fe68.6B25.7Y5.7) 100-xNbx (x = 3-5 at.%) are expressed approximately with a unified simple composition formula: (Fe8B3) 1 (Y, Nb) 1. The (Fe68.6B25.7Y5.7) 97Nb3 bulk metallic glass has the largest glass forming ability with the following characteristic parameters Tg = 907 K, Tx = 1006 K, Tg / Tl = 0.644, = 0.434, and longness t = 22 mm. The combination of the cluster line rule and the minor-alloying principle is a promising new route towards the quantitative composition design of multi-component metallic glasses.