Results from theoretical and experimental studies of cycle-by-cycle variations of flame propagation periods during the combustion in spark ignition engine are reported herein. Theoretical considerations show that cyclic variations depend on mixture turbulence and homogeneity characteristics. During an experimental work two ionization probes have been used to define the flame formation and total propagation periods and to enable visual observation of flame propagation duration in a series of successive engine cycles. The effects of main factors (turbulence level, compression ratio and mixture homogeneity) affecting flame kernel formation and flame propagation cyclic variations are discussed in the paper.One of the main conclusions is that a high turbulence reduces variations of developed flame propagation period, but an improved mixture quality could be important for the flame initiation. Both factors decrease total cyclic variations, though the effect of turbulence is greater.