Investigations comparing tryptophan fluorescence of mitochondrial actin-like protein with that of skeletal and smooth muscle actins have shown that the mitochondrial protein is characterized by a fluorescence spectrum peak at a longer wavelength (337 nm), by a certain broadening of this peak (56 nm) and by a reduction in the lifespan of the excited state of tryptophanyls (2.7 ns). The data obtained suggest the existence of peculiarities in the structure of mitochondrial actin-like protein.