When a signal at the nominal frequency of 76 GHz and a local oscillation (LO) at the frequency of a few gigahertz were both applied to a YBa2Cu3O7−yweak link immersed in liquid nitrogen, the former mixed with the harmonics of the latter giving rise to output at the intermediate frequency (IF) of about 150 MHz. The highest observed harmonic number was 51. Without exhaustive effort to optimize, the typical IF output power referred to the mixer output ranged between −103 and −112 dbm while the IF signal‐to‐noise ratio ranged between 16 and 4 db, depending strongly on the local oscillation power, the dc bias current, and the signal power. Reported in this letter are the experimental details as well as the requirements for a superconducting weak link to be a harmonic mixer.