These studies were carried out to estimate the parameters of egg production curve of McMillan Model (1970 a, b) and to try genetic analysis of the parameters and some other parameters, and finally to investigate the usefulness of egg production curve. A total of 477 hen records from one strain (A1, 1977; A2, 1978) of S. C. White Leghorn at College of Agri., Seoul National Univ, and 388 hen records from two strains (C, D, 1975) of Rhode Island Red at Dejon Branch Farm, National Animal Breeding Experimental Station were used in these studies. The parameters of egg production curves in all from fitting the model to mean egg production on monthly time scale were from 29.45 to 36.04 for the potential maximum monthly egg production, from 1.226 to 2.918 for the rate of increase, from 4.773 to 5.563 for the initial month of egg laying, from 0.023 to 0.053 for the rate of decrease. Heritability estinates of the parameters from combined sire and dam variance components in the whole population were 0.18 for the potential maximum monthly egg production, 0.11 for the rate of increase, 0.29 for the rate of decrease, 0.28 for the initial month of egg laying, 0.31 for the peak production, 0.46 for the total egg production (from the day of first egg to 36kws). Genetic correlations were 0.23 between rate of increase and rate of decrease, 0.60 between rate of increase and initial month of egg laying. There were high positive genetic correlation (0.80%) between peak production and total egg production. Comparisons of egg productions by extending production periods through egg production models were interesting.