We have studied the TiO₂ doping effects on the flux pinning behavior of an MgB₂ superconductor synthesized by the in-situ solid-state reaction. From the field-cooled and zero-field-cooled temperature dependences of magnetization, the reversible-irreversible transition of TiO2-doped MgB₂ was determined in the H-T diagram (the temperature dependence of upper critical magnetic field and irreversibility line). For comparison, the similar measurements are also obtained from SiC-doped MgB₂. The critical current density was estimated from the width of hysteresis loops in the framework of Bean’s model at different temperatures. The obtained results manifest that nano-scale TiO₂ inclusions served as effective pinning centers and lead to the enhanced upper critical field and critical current density. It was concluded that the grain boundary pinning mechanism was realized in a TiO₂-doped MgB₂ superconductor.