Mercurial-bound metallothioneins (MTs) induced in kidney of rat after oral intake of HgCl2 were characterized with the developed hyphenated techniques including reverse phase chromatography (RPC) coupled with inductively coupled plasma mass spectrometry (ICPMS) and electrospray ionization mass spectrometry(ESIMS). After being purified with size-exclusion column (Sephadex G-75) and dialysis (M<1000 Da), the extracts was separated with a narrow-bore reverse phase column and eluted by increasing methanol at gradient mode. The MT polymorphism with different binding-metal (including Hg, Cu and Zn) species was interpreted by the measured masses at the vicinity of apexes in total ion current (TIC) of ESIMS and the reference data of apo-MTs reported.The results indicated that many Hg-binding MT species existed in the polluted rat kidney.