In this research, a total of 27,241 edited records from four distinct files of calving, pedigree, insemination and production collected by Iranian animal breeding center, from 1984 to 2007 were used to study effects of inbreeding, on various traits in 543 herds of Iranian Holsteins. The traits was age at first freshening, days of productive life, total milk, mean fat percent, mean calving interval, relative net income (lifetime profit) and RNI per day (profit per day of lifetime). Preparing and required edition of the data was undertaken by Foxpro and Excel software.  For calculating the inbreeding coefficients, Pedigree software (Sargolzaee, 2000) was utilised. The overall average inbreeding coefficients was 1.63%. Relative net income of per cow was calculated by Shadparvar equivalent (1999) based on the costs and incomes of 2007, from Sefidroud (first farm) and Maghan (second farm) farms. The effects of inbreeding on the traits were analyzed by a model (with inclusion of herd and first calving year) by Proc GLM of SAS program. In the model, herd and first calving year effects on all traits was highly significant (P<0.001). Inbreeding effect on age at first freshening, total milk, RNI and RNIPD was highly significant (P<0.001). This effect was not significant on productive life, mean fat percent and mean of calving interval. The result of this research showed that the average inbreeding coefficient in Iranian Holsteins was lower than the other populations, which could be the result of the avoidance of farmers from inbreeding and also because of incomplete or wrong information. This research also revealed that the price level of products and nourishment costs could affect the profitability of inbred cow such that an inbred cow is harmful in one herd but is useful on the other herd condition.