In this work, visual observation as well as the probability density function and the standard deviation of the pressure drop fluctuation were used for determination of the boundary of trickling-to-pulsing flow transition. Extensive experimental work was carried out with air and three liquid media on four kinds of packings. Experimental results indicate the transition depends on the physical properties of liquid (viscosity and surface tension), gas and liquid flow rates as well as the size and shape of packing particles. The Baker coordinates (Baker, 1954) used in the flow map as proposed by Charpentier and Favier (1975) was examined. It is found that application of the flow pattern map in this form is of rather limited universality. Two new correlations were proposed with satisfactory prediction of the liquid flow rates for the transition of trickling-to-pulsing flow.