<p>The two-dimensional material that emerged with the discovery of graphene has attracted great attention due to its interesting optical, electrical and mechanical properties. In recent years, especially two-dimensional (2D) perovskite oxides have attracted attention due to their ability to exhibit insulating, semiconducting or conducting properties. Dion-Jacobson perovskite oxides from the 2D perovskite oxide family have been intensively investigated due to their remarkable chemical and physical properties such as giant magnetoresistance, high-temperature superconductivity, ferroelectricity and photocatalytic activity. In this review, the properties, synthesis methods and device applications of calcium niobate nanosheets (KCa₂Nb₃O₁₀ commonly referred to as CNO), one of the Dion-Jacobson perovskite oxides, are discussed. Promising results have been obtained in Ultraviolet (UV) detection and photocatalytic applications with CNO structures. However, when the literature was examined, no review article was found that examined CNO nanosheets in detail. It is thought that; this study will fill this gap in the literature.</p>