There is a need for photocatalysts with efficient photocarrier separation to address issues with environmental pollution. Photocarrier separation is largely determined by the orbital composition near the band edge. Here, we investigate Zn4B6O13 as an efficient photocatalyst for photodegradation of tetracycline. Theoretical calculations of Zn4B6O13 show that the valence band near the Fermi level is composed of d and p orbitals whereas the bottom of the conduction band is composed of s and p orbitals; thus, a large value of mh*/me* is derived from the band dispersion. The characteristics of this orbital composition promote separation of photoexcited carriers, leading to a high transfer efficiency of the catalyst. Moreover, photodegradation experiments demonstrate that the photocatalytic activity of Zn4B6O13 is approximately 5.2 times as high as that of SnO2. This study provides insights that might aid the development of novel borate-based environmental photocatalysts with superior performance.