Er3+-doped strontium gadolinium gallium garnet (SrGdGa3O7) single-crystal was grown by Czochralski method. The Er3+ concentration in the crystal was determined as 4.2 x 10(21) ions/cm(3) by inductively coupled plasma atomic absorption spectroscopy. Refractive index of the crystal was measured at the wavelengths of 633, 1311 and 1553 nm by prism coupling technique. The results show that the crystal is a positive uniaxial crystal with a birefringence of 0.01, and the Sellmeier equation reported previously for the crystal doped with Nd3+ is also valid for the one doped with Er3+. Unpolarized absorption spectrum of the crystal was measured at room temperature and the Er3+ absorption cross-section spectrum was calibrated from it. The Er3+ spectroscopic properties were studied by Judd-Ofelt theory. Some fundamental spectroscopic parameters were obtained that include absorption coefficient and cross-section spectral distributions, electronic transition oscillator strength, Judd-Ofelt parameters, fluorescence branch ratio, transition probability, radiative and fluorescence lifetimes, and quantum efficiency.