Results are presented on the microwave intermodulation distortion (IMD) measured in high-temperature-superconducting YBa 2 Cu 3 O 7 - Φ engineered grain boundaries fabricated on bicrystal substrates. The two-tone IMD at 4.4 GHz of thin YBCO plain films without engineered grain boundaries and films with engineered bicrystal grain boundaries of misorientation angles from 2° to 24° was measured as a function of microwave power and temperature in a suspended microstrip resonator configuration. The microwave power dependence of the IMD of the plain films and the films with grain boundaries is compared. The long Josephson-junction effects of high-angle grain boundaries were studied. The connection between the results for the microwave impedance of YBCO grain boundaries and for the IMD has been modeled. We find that for grain boundaries of less than 7.5°, the IMD is indistinguishable from that of the plain film.