While irreversible aggregation or amyloid formation of denatured proteins are well known and studied in detail, the reversible oligomerization (RO) states of some monomeric proteins at high temperature have been recently discovered by DSC analysis. In this article, the RO states of horse cytochrome c and envelope protein domain 3 from dengue 4 virus were reviewed, and the essential points for the DSC analysis for such self-association/dissociation process were briefly introduced. The significance of RO was discussed as a key process for the kinetics of aggregation and/or amyloid formation, and the importance of the concentration dependence check was suggested for DSC analysis even for monomeric proteins.