Mn2.02Co0.98O4 ceramic with tetragonal spinel structure was prepared by solid-state coordination reaction method. The phase and microstructure were studied using X-ray diffractometer (XRD) and transmission electron microscope (TEM), respectively. The results show that the Mn2.02Co0.98O4 ceramic exhibits tetragonal spinel structure owing to imperfect quenching. Several kinds of defects were formed in the sample due to the phase transition from cubic spinel at high temperature to tetragonal spinel at room temperature. Two types of {112} twin wall were found in the quenched Mn2.02Co0.98O4 ceramic. The presence and the characteristics of twins were investigated. The twins arranged in a cyclic triangle form and the twin boundaries were parallel to (112) plane or ((1) over bar 12) plane. The possible mechanism for twinning arrangement in the triangle form was proposed according to some crystal geometry model analysis.