We succeeded in the complete detwin of (Y, Gd) BCO coated conductors using a newly developed in-situ tensile apparatus at high temperature. The intensities of (020) and (200) peaks in a longitudinal and a transverse directions of the tape measured by XRD were similar to each other for usual (Y, Gd) BCO coated conductors before annealing. However, the (200) peak disappears for the longitudinal direction after annealing under the tensile stress. It means that the coated conductors are detwinned by annealing under the tensile stress. We found that T-c linearly decreases with increasing strain for the B-domain (b-axis). This behavior is similar with a uniaxial-pressure effect in (Y, Gd) BCO single crystals. However, the strain dependence of T-c for the A-domain (a-axis) behaves as a power-law function, whereas the uniaxial-pressure dependency of T-c for the a-axis is reported to be linear. In addition, the strain dependencies of J(c) are similar with those of T-c