The optical rectification in a semiparabolic quantum well is theoretically investigated. The electronic states in a semiparabolic quantum well are calculated exactly, within the envelope function and the displaced harmonic oscillator approach. The nonlinearity resulting from the asymmetry of the confining potential is studied in the lowest order. The numerical results for the typical AlxGa1-xAs/GaAs material show that the large optical rectification coefficient decreases with increasing confining potential frequency of the semiparabolic quantum well. Moreover, the optical rectification coefficient also depends sensitively on the relaxation rate of semiparabolic quantum well system. (C) 2005 Elsevier Ltd. All rights reserved.