This study was undertaken as an effort to improve our understanding of the mechanisms of pulsating flame spread over liquids. A holographic interferometry technique was applied to obtain a time series of simultaneous temperature profiles in gas and liquid phases for pulsating spread over propanol. Liquid motion at the free liquid surface was visualized using a particletrack technique and recorded with a high speed, high resolution video-camera from which pulsation frequency and flame behavior were analyzed. Our experimental results support the hypothesis that the primary control mechanism of pulsating spread is subsurfaceliquid flow, while the effect of gas-phase convection is secondary even though it governs flame pulsation. To evaluate this interpretation, two dimensional incompressible flow equations were numerically solved and fluid dynamic structure was simulated as a function of fuel-layer thickness. The calculation results explain the present and NASA's experimental results and support our proposed mechanism of pulsating spread.