An experimental study investigating the cyclic variation of the internal air motion has been made in a motored engine having a cup-in-piston combustion chamber. The engine used for this study has a transparent quartz liner and a transparent plastic (acrylic resin) piston. The light source used to produce sheet was a 4 watt argon ion laser with continuous wave beam. The brightness irregularity patterns of particle groups were recorded photographically by a NAC E-10 high speed camera and the bulk flow fields inside of the combustion chamber have been measured at both planes parallel and vertical to the piston crown by means of image processing technique.This paper for the first time reveals the continuous cycle-resolved two-dimensional bulk flow fields inside of the combustion chamber around the compression TDC. Also, comparison between cycle-resolved and ensemble-averaged flow patterns has shown that ensemble-averaged flow pattern may become a artificial one if there exists the large effect of the cyclic variation. Moreover, by examining into the rms of the variation component and the ratios of the rms to ensemble-averaged velocity under with/without swirl conditions, it is found that the ratios of the rms to ensemble-averaged velocity can be used for evaluating the effect of the cyclic variation on the flow fields.