The interaction of two lanthanides Cerium (Ce 3+ ) and Gadolinium (Gd 3+ ) and two heavy metal ions Manganese (Mn 2+ ) and Zinc (Zn 2+ ) with various biological proteins Bovine Serum Albumin, Human Serum Albumin, β-lactoglobulin, Myoglobin and Ovalbumin were studied by using mobility shift affinity capillary electrophoresis. The used ACE method offers fast operation using shorter capillary, small injection volume, adequate short rinsing protocol and lower concentration of samples. The normalized difference of mobility ratio (ΔR/R f ) was used to investigate the possible interaction. All interactions were summarized as ΔR/R f chart and compared. For heavy metal ions, the interactions of Mn 2+ with all proteins were significant with negative ΔR/R f values except with Myoglobin (MB) as its ΔR/Rf close to zero (0.002± 0.03) and one of its cnf(ΔR/R f ) values intersect the zero line indicates insignificant interaction. Very weak interactions between Zn 2+ and all proteins were detected with small +ΔR/Rf values and confidence intervals intersected the zero line. For lanthanides, Cerium (Ce 3+ ) showed weak interactions with BSA, HSA. Whereas, strong interactions were observed with MB and BLACT. Gd 3+ showed almost insignificant interactions with most of the tested proteins except MB, it showed strong interaction with MB in a manner similar to Ce 3+ . Influence of the coordination number of the metal ions and multiple binding sites within the proteins on the signs of ΔR/R f values were discussed in details. Furthermore, the change in protein peak shape was found to be as evident for a possible conformational change for the proteins and their affinity to the metal ions.