The ${eta}$-subunit of high-voltage-activated (HVA) calcium channels is essential for the regulation of expression and gating. On the other hand, various reports have suggested that ${eta}$ subunits play no role in the regulation of lowvoltage-activated T-type channels. In addition there has been no clear demonstration of a physical interaction between the ${alpha}$-subunit of T-type channel with ${eta}$-subunit. In this study, we systematically investigated the interaction between $Ca_V{alpha}$ and $Ca_V{eta}$. The four $Ca_V{eta}$ isoforms were expressed in a bacterial system and purified into homogeneity, whereas the ten types of $Ca_V{alpha}$ alpha interaction domain (AID) peptides were chemically synthesized. All possible combinations of $Ca_V{alpha}$ and $Ca_V{eta}$ were then tested for by in vitro immunoassays. We describe here the identification of a new interaction between $Ca_V3.3$ and $Ca_V{eta}$ proteins. This interaction is of low affinity compared to that between the AID of the HVA ${alpha}$-subunit and the alpha-binding pocket (ABP) site of the ${eta}$-subunit. The AID peptide of HVA channel exerted no effect on the $Ca_V3.3-Ca_V{eta}$ interaction, thus demonstrating that another site not in the ABP of $Ca_V{eta}$ protein played a role in binding with $Ca_V3.3$. This is the first demonstration of an ${alpha}-{eta}$ subunit interaction in a T-type calcium channel.