Reduction in the cycle-to-cycle variation (CCV) of combustion in internal combustion engines has been required because CCV affects fuel consumption, emissions and drivability. CCV becomes stronger at low load or lean / diluted burn conditions. Specifically, the factors that cause CCV of combustion are supposed to variations of in-cylinder flow, fuel distribution, temperature distribution, residual gas distribution and ignition energy in each cycle. However, it is impossible to measure and analyze minutely these factors in a production engine. In this study, CCV of the combustion and in-cylinder phenomena in the same cycle of PFI gasoline engine were investigated by using an optical single-cylinder engine. This optical engine can observe the whole combustion chamber by the quartz glass cylinder and pent-roof window. CCV of flow in the cylinder during continuous 45 firing cycles was measured by Time Resolved Particle Image Velocimetry (TR-PIV) technique. The in-cylinder flow was measured at an intervals of 2 crank angle degrees during intake to compression strokes using a dual-cavity, high frequency Nd:YLF laser. The instantaneous flow was converted to a time-averaged flow by low pass filtering in order to remove the high frequency component and analyze CCV of flow from-cycle-to-cycle. CCV of fuel and temperature distributions at IVC and just before ignition timing were measured by Planer Laser Induced Fluorescence (PLIF) technique. The fourth harmonic generation of a dual-cavity Nd:YAG laser was used for the excitation light source. 3-pentanone was used as a PLIF tracer, which was mixed with iso-octane and injected to the intake port. These two visualization techniques were synchronized in the measurement of combustion during continuous firing cycles. As a result, it was confirmed that CCV of flow and fuel distribution are strong in low load conditions. Especially, CCV of flow is strong at intake stroke and before ignition timing.