A novel nonlinear optical amino acid derivative,L‐pyrrolidone‐2‐carboxylic acid (L‐PCA), has been studied for the application of UV generation by frequency upconversion of laser radiation.L‐PCA is relatively easy to grow from solution to a large size, typically ∼40×20×20 mm3, by a slow cooling method. This crystal is chemically stable because the crystal lattice is composed of a network of hydrogen‐bonded molecules.L‐PCA has a wide transparency extending to the UV region (the cutoff wavelength is 260 nm) and is therefore a good candidate for the second‐harmonic generation (SHG) of Nd:YAG laser radiation (1064 nm). The nonlinear‐optical coefficientd14was measured to be 0.22 pm/V, and the measured phase‐matching angles agreed with values calculated using refractive index data. The effective nonlinear optical coefficientdeffof the type‐I phase‐matched SHG has also been measured to be 0.20 pm/V. UV generation down to 266 nm was achieved by phase‐matched SHG inL‐PCA crystals. ©1995 American Institute of Physics.