Abstract: To investigate the formation and transport processes of smoke aerosols inside a cigarette during smoking, in-situ sampling and online characterization methods for smoke aerosols inside a lit cigarette were developed based on an aerosol microprobe sampling system and an aerosol particle size spectrometer, which enabled the online characterization of the transport process of smoke aerosols inside a cigarette. The results showed that: 1) The aerosol microprobe sampling system allowed the precise control of the position, time sequence and flow rate of in-situ aerosol sampling, thereby achieved in-situ sampling of smoke aerosols inside a cigarette. 2) The in-situ aerosol sampling and online characterization method exhibited good stability, with reliable aerosol detection accuracies for both particle number concentration and count median diameter (CMD) at different positions inside a cigarette. The ranges of relative standard deviations (RSDs) were 5.73%-10.22% and 2.34%-4.69%, respectively. 3) The in-situ sampling and online characterization methods were applied to the puff-by-puff characterizations of smoke at 3 test locations along the cigarette rod: the tobacco section, the junction between the tobacco section and the filter, and the smoke outlet end of the filter. Puff-by-puff variations in particle number concentration and CMD of smoke aerosols at these different positions inside a burning cigarette were obtained. This in-situ sampling and online characterization methods for cigarette smoke aerosols with excellent stability were convenient to operate, which could provide references for routine study of the formation and transport mechanism of cigarette smoke aerosols.