Ribonucleases are the best-studied proteins in the world of biochemistry. Today, some of these proteins are giving new surprises. It is known that onconase and barnase are water-soluble proteins with antitumor action toward human tumor cell lines. Unfortunately, exact mechanism of the RNases cytotoxicity is still unclear. Here, the structural key, namely the hydrophobic segment, which allows to explain many biological effects of onconase and barnase, was reported.The main aim of this investigation is to show that onconase and barnase have special hydrophobic properties, which participated in the apoptosis of tumor cells induction. Here, a clear evidence that onconase and barnase can be mimetics of proapoptotic Bax protein, which belong to the Bcl-2 family proteins, was obtained. It is may be useful for explanation of the mechanism of apoptosis induction.