This study was carried out to investigate factors affecting the shape of the lactation curve and to estimate milk yield of dairy cattle using Wood`s model (Yn= An^b e^-cn). Data used for this study included a total of 963 lactation records of Holstein cows from 3 dairy farms from 1972 to 1987. The results obtained from this study are summarized as follows : l. The value of parameter a for the lactation curve under dry-period length was highest for 60-75 dry-period length(3.3763), the values of parameter b and peak-month were highest for 45-60 dry-period length (0.4919, 2.34) and the value of parameter c was lowest for 60-75 dry-period length(0.1600). Maximum daily milk yield and total milk yield were highest for 45-60 dry-period length. 2. The values of parameter a for the lactation curve under days open was highest for 150 days open (3.4751), the value of parameter b and peak-month were highest for 120 days open (0.5640, 2.50) and the value of parameter c was lowest for 60 days open. The values of persistency decline but maximum daily milk yield and total milk yield increase with advancing days open. 3. The estimation factors of the early stage of lactation were lowest for 60-75 dry-period length, and the estimation factors of he late stage of lactation were highest for 45-60 dry-period length. 4. The estimation factors of monthly milk yield according to days open and calving season were higher in the late stage of lactation than in the early stage of lactation.