This study conducted at Deir Al-Hajar Station during the season 2010-2011 to describe the lactation curve of Shami cattle and determine factors affecting its shape compenents. 1120 records of 356 Shami cows collected between 1997 – 2010 were used. Data were subjected to general linear model, and the analysis of variance used to determine the effect of factors. Duncan test was used to compare the means using SAS system (1996) and Incomplete gamma functions were used to estimate the parameters of lactation curve (a, b and on the basis of daily yield of milk. Results indicated that the average values of the gamma parameters were 2.14 ± 0.01 kg for a (beginning of milking ), 0.61 ± 0.02 kg for b (increasing milk production up to peak) and - 0.23± 0.01 kg for c (decreasing milk production from peak to dry). The effect of calving year was significant (p<0.01) on a, and (p<0.05) on b and (p<0.001) on c. The effect of age at calving and sex of calf was significant (p<0.01) on a but non significant on b and c. Season of calving, parity, and interaction between age and parity was not significant on all parameters. It was concluded that improving the productive performance of Shami cattle, requires applying a long term genetic improvement program to select the best herd.