The aim of this study was to investigate the effects of inbreeding on economic important traits in Holstein dairy cattle using a meta-analysis to assess the real amount of inbreeding depression on each trait. This research was conducted using two statistical software; SAS for all investigated (productive and functional) traits and comprehensive meta-analysis (CMA), only for productive traits. To do this, studies published in valid journals from 1930 to 2015, were used. In the first method, studies were weighted by sample size while in the second method, inverse of standard error square (1/SE2) was applied. Results obtained from the first method, a mixed model including fixed effects of investigated population and parity number and random effect of study, showed that by a one-percent increased in inbreeding, milk, fat and protein yields decreased 30.95, 1.20 and 0.99 kg per cow per lactation. Inbreeding depression for lactation 2+ was higher than that of first lactation; the losses in productive traits (milk, fat and protein) for first lactation cows were 24.36, 0.92 and 0.76 kg, respectively whereas the correspondence values for lactation 2+ were 33.49, 1.32 and 1.07 kg, respectively. The results from CMA (a random model including of the effect of study) were lower hat those of mixed model, partially due to a limited number of studies and publication bias. Results from mixed model revealed that somatic cell score increased 0.0042 and 0.0046 score per one percent increased in inbreeding for the first lactation cows and in overall, respectively. Age at first calving, gestation length and productive life showed an increase of 0.48 day, 0.04 day and a decrease of 7.07 day per one-percent increase in inbreeding per cow per lactation, respectively. In addition, calving interval increased by 0.26, 0.53 and 0.31 day per one-percent increase in inbreeding per cow for lactation 1, 2+ and overall, respectively. Generally, on the base of findings from present study we can conclude that in order to investigate the economic consequences of inbreeding corrected values from a meta-analysis instead of arithmetic means which led to biased estimates of inbreeding depression, can be used. Keywords: Meta-analysis, Inbreeding depression, Holstein, Production traits