In this study, we apply a hybrid DFT functional, MPW1LYP, to make a comparison between MeSNO and MeSeNO. Due to the mesomeric effect and negative hyperconjugation, Se-nitrososelenols seem to be more unstable than S-nitrosothiols regarding unimolecular decomposition. Interestingly, however, the barrier of the transnitrosation reaction of MeSeNO is larger than that of MeSNO, disregarding nucleophiles in the gas phase. Using the polarizable continuum model to consider the water solvent effect, the transnitrosation reactions of MeXNO and YMe- (X = S, Se; Y = S, Se) are found to undergo concerted reactions, in sharp contrast to the two-step reaction pathways concluded in the gas phase. Moreover, the barriers of the transnitrosation reactions of MeSNO for nucleophiles SMe- and SeMe- from the gas phase to the aqueous solution are found to be decreased, while the transnitrosation reactions of MeSeNO are essentially barrierless in aqueous solution.