To reveal clearly the doping effect on the growth and properties of KDP single crystals, bulk concentration 1.0 mol% and 5 mol% of MnCl2 (Mn2+) was doped in KDP single crystals by using slow evaporation method. Interesting results like nucleation, rate of growth, and defect formations were found during the investigation. The different stages of live growth are recorded with the help of inverted microscope. Powder X-ray diffraction (XRD) analyses confirm the tetragonal structure of pure and doped KDP. The variation in the intensity of diffraction peaks shows the minute change in lattice parameters in correlation with morphology of varying Mn2+ doping concentrations. The above studies further reveal that the structure and morphology of the doped crystals are slightly distorted compared to the pure KDP crystal. The optical properties of the grown crystals have been investigated by using UV–visible spectra. The band gap energy for the doped KDP crystals was calculated from optical transmission spectrum.