We report on a picosecond YBa2Cu3O7−&dgr;detector for far‐infrared radiation. The detector, consisting of a current carrying structure cooled to liquid‐nitrogen temperature, was studied by use of ultrashort laser pulses from an optically pumped far‐infrared laser in the frequency range from 25 to 215 cm−1. We found that the sensitivity (1 mV/W) was almost constant in this frequency range. We estimated a noise equivalent power of less than 5×10−7W Hz−1/2. Taking into account the results of a mixing experiment (in the frequency range from 4 to 30 cm−1) we suggest that the response time of the detector was few picoseconds.