Time series analyses of diesel exhaust gas emissions under transient operation were carried out using a gas sampling system to efficiently collect all exhaust gas over several cycles. The effects of fuel properties and other operating parameters on the exhaust emissions under transient runs were analyzed. The results showed that THC increased abruptly to 2-6 times the steady-state concentration immediately after the start of acceleration and then decreased to the steady-state values after 70-200 cycles. At acceleration, NOx increased abruptly to about 80% of the steady-state value, and then increased gradually to reach the steady-state values after 60-500 cycles. The behaviors of THC and NOx during transient operation can be described by the exponential functions of the elapsed cycle numbers and the final emission concentrations. The concentrations of CO, CO2, O2, and smoke changed abruptly to the steady-state values at the start of acceleration. One of the dominant factors affecting the gas emissions during transient operations is the deposition of fuel on the combustion chamber wall.