Abstract: The first part of this paper concerns with optimum reflux ratio of packed column for close-boiling fractionation. A correlation is proposed to find the NTU at finite reflux and from which a graph representing the optimum reflux ratio is derived. It is found that the maximum value of optimum reflux ratio is about 1.4Rm. The second part of this paper concerns with optimum ratio of column diameter to packing size. Experimental work has been conducted with four laboratory columns of 20, 28,32 and 44 mm in diameter respectively, the height of packed bed ranging from 1020 to 1475mm, the packing used being 2.5x2.5 mm angular helices and the testing system to be n-heptane-methylcyclohe-xane. The true separation efficiency (i. e. true HTU or true NTU per meter of bed height)is evaluated from the experimental composition profile by discarding the end effect at the top and the bottom ends of packing. By plotting the true separation efficiency versus the ratio of column diameter to packing size, all the curves at constant vapor velocity exhibit an optimum reflux ratio with nearly identical value. The optimum reflux ratio for this packing is found to be 13-14 which is in rough agreement with that for ordinary or industrial size of packing.