Understanding the structure-property relationship in functional materials is crucial as microstructural features such as nano-precipitates, phase boundary, grain boundary segregation, and grain boundary phases play a key role in their functional properties. Atom probe tomography (APT) is an advanced analytical technique that allows for the three-dimensional (3D) mapping of atomic distributions and the precise determination of local chemical compositions in materials. Moreover, it offers sub-nanometer spatial resolution and chemical sensitivity at the tens of parts per million (ppm) level. Owing to its unique capabilities, this technique has been employed to uncover the 3D elemental distributions in a wide range of materials, including alloys, semiconductors, nanomaterials, and even biomaterials. In this paper, various kinds of examples are introduced for elucidating structure-property relationships on functional materials by utilizing the atom probe tomography.