Minor alloying is a useful approach for promoting glass forming ability (GFA) of metallic glasses. U-Co metallic glasses can be achieved in a wide composition range, but their GFAs are very poor. This study is aimed to increase the GFA in U-Co system by minor alloying. Sn, Si, Be, Cu, Pd, Y and Zr were selected as different-typed minor alloying elements in U69.2Co30.8 alloy. The glassy U69Co30M1 (M=Sn, Si, Be, Cu, Pd, Y, Zr) ribbon samples were prepared by melt-spinning with a copper roller, and their phase formation and thermodynamics were investigated by X-ray diffraction (XRD) and differential scanning calorimetry (DSC) techniques. The results indicate that, Sn element significantly improves the GFA, Si displays the second improvement, Be and Cu are slightly effective while Pd, Y and Zr deteriorate the GFA. Based on the combination of the melting behavior change reflected by the DSC result, and the relationship between the GFA and the melting temperatures, electro-negativities, atomic sizes of M elements as well as mixing-enthalpies of M-C, the effect of the minor alloying on the GFA in U-Co system should be attributed to the variation of both metallic liquid stability and the crystallization driving force.