Abstract: Mass spectra of Roussinate anions with various cation (such as K~+ or R_4N~+)has been obtained under appropriate operating conditions and based on linkedscan information of metastable transition in 1st FFR and precise mass deter-minations the fragmentation pathways are proposed. It is found that theskeleton structure of the red Roussinate anion is more stable than that ofblack Roussinate anion. It is interesting to note that rearrangement reaction with transfering ofmethyl radical in tetramethyl ammonium cation to bridged sulfur atom occursduring evaperaton of (CH_3_4N_2Fe_2S_2(NO)_4, forming red methyl Rous-sinate: In this paper we will provide some significant information regarding tothe rationalization of the interconversion reaction between Roussinate aniousunder certain condition.