Picosecond pulses have been generated over a broad spectral range with passive mode locking of dye lasers pumped by a long‐pulse XeCl laser. The rapid reduction of pulse duration to less than 10 ps was confirmed to occur within a few tens of round trips. The characteristics of mode locking were intensively investigated at the multiple wavelengths of rare‐gas halide lasers such as KrF, ArF, and XeCl lasers, resulting in pulse durations of 5.5 ps at 497 nm and 7 ps at 580 nm, respectively.