α-Actinin is a regulatory protein located on Z-lines. In vitro, α-actinin has two functions: 1) induction of superprecipitation (SPPT) of Straub-type actomyosin; and 2) induction of gelation of actin solutions. This paper describes the effects of pressure on the structure and biochemical function of α-actinin. From changes in the fluorescence and circular dichroism (CD) spectra, and in the aliphatic surface hydrophobicity of pressurized α-actinin, it seems that the changes in the structure of α-actinin pressurized to over 400 MPa are irreversible. We found that the SPPT-enhancing activity of α-actinin and the STTP-associated ATPase activity were more or less lost from α-actinin pressurized to about 400 MPa, and the addition of α-actinin pressurized to over 300 MPa increased the viscosity of an actin solution only slightly, so it seems that the SPPT-inducing activity of α-actinin is highly correlated with its actin gelation activity, rather than with its ATPase acceleration activity. The results of this study will be useful for better understanding the mechanisms underlying pressure-induced meat tenderization.