A large single crystal (18×40×15 mm3) of a new nonlinear optical material ‘‘chalcone derivative’’ has been grown by an evaporation method. This crystal was relatively easy to grow to a large size and was chemically stable. The cutoff wavelength was 430 nm. The calculated phase matching angles for the second‐harmonic generation (SHG) of Nd:YAG lasers agreed with the experimental data. Effective nonlinear optical coefficientsdeffof type I and type II for SHG have been measured to be 3.5 pm/V for type I and 5.7 pm/V for type II.