The inclusions in conventionally grown KD2PO4 (DKDP) crystals are investigated. The inclusions are captured by a light-scattering technique. The sizes are determined by an optical microscope and a transmission electron microscope (TEM), and the compositions are analyzed by time of flight secondary ion mass spectrometry (TOF-SIMS) and an energy dispersive spectrometer (EDS). Two kinds of inclusions are observed in the DKDP crystals: a submicron-scale inclusion and a micron-scale inclusion. The typical submicron-scale inclusions contain growth solution, and their sizes range from tens to hundreds of nanometers, whereas the micron-scale inclusions contain growth solution and the metal element Na, and the sizes are tens of microns. The possible formation mechanisms of the inclusions are discussed, and the influence of the inclusions on laser-induced damage behaviors are analyzed and discussed.