Liquid mixing on sieve and packed sieve trays was studied in a 300 mm diameter air- water column. The degree of mixing was measured in terms of a longitudinal eddy diffusivity (De) and Peclet number (Pe) by a steady-state tracer technique. It was found that by adding a 25.4 mm thick mesh packing on a sieve tray, the eddy diffusivity decreased significantly. The effects of packing heights on liquid mixing were also investigated and it was found that the eddy diffusivity decreased further with greater packing heights. The experimentally measured De values were correlated. The results indicate that eddy diffusivity is influenced by liquid rate, gas superficial velocity and packing height. The correlation is best represented by (De)(0.5) = 0.0275 + 0.0206L’ + 0.00378V(1.71) - 0.321Hp(0.835) The equation can be used to quantitatively calculate the degree of liquid mixing so that the causes for the enhancement of tray efficiency by packing can be determined.