Effective prevention from the leakage of Polychlorinated Biphenyls (PCBs) requires the rapid analysis with on-line detection, but conventional methods require extensive analytical time (several days per sample) and are thus unsuitable. The objective of the research reported here was to develop the Laser Ionization / Ion Trap Storage / Time of Flight Mass Spectrometry (LI-IT-TOFMS) capable of monitoring PCBs within 1 min/sample, as applied to exhaust gas and the atmosphere of the disposal work environment. The achievable PCBs sensitivity for on-line measurement was found to be in the pptV range (< 0.01 mg/m³_N) by means of comparison with conventional gas sampling and gas chromatograph - mass spectrometry (GC-MS). A satisfactory proportional relationship was confirmed between laser-based and conventional results for PCBs. We measured the exhaust gas in a PCBs treatment plant (hydrothermal decomposition and container treatment processes) by using the PCBs monitoring system, confirming that PCBs monitoring is possible without interference from either the main gas composition or minor coexisting substances. Accordingly, the LI-IT-TOFMS method is a useful method for the trace analysis of PCBs in exhaust gas.