Bi2O2Se oxyselenides, characterized with intrinsically low lattice thermal conductivity and large Seebeck coefficient, are potential n-type thermoelectric material in the mediate temperature range. Given the low carrier concentration of similar to 10(15) cm(-3) at 300 K, the intrinsically low electrical conductivity actually hinders further enhancement of their thermoelectric performance. In this work, the isovalent Te-substitution of Se plays an effective role in narrowing the band gap, which notably increases the carrier concentration to similar to 10(18) cm(-3) at 300 K and the electron conduction activation energy has been lowered significantly from 0.33 to 0.14 eV. As a consequence, the power factor has been improved from 104 mu W.K-2.m(-1) for pristine Bi2O2Se to 297 mu W.K-2.m(-1) for Bi2O2Se0.96Te0.04 at 823 K. Meanwhile, the suppressed lattice thermal conductivity derives from the introduced point defects by heavier Te atoms. The gradually decreased phonon mean free path reflects the increasingly intense phonon scattering. Ultimately, the ZT value attains 0.28 for Bi2O2Se0.96Te0.04 at 823 K, an enhancement by a factor of similar to 2 as compared to that of pristine Bi2O2Se. This study has demonstrated that Te-substitution of Se could synergistically optimize the electrical and thermal properties thus effectively enhancing the thermoelectric performance of Bi2O2Se.