Hanwoo is an important livestock resource in Korea. Its genetic improvements of economic traits have mainly focused on the steers in the past. However, there is a great necessity to extend the breed improvement programs to the cows as well. Therefore, the objective of this study was to investigate the effects of various environmental factors (person taking the measurement, region, year of measurement, month of measurement, image interpreter, birth-year and birth-year) on ultrasound measured carcass traits. A total of 27,215 ultrasound measurements of carcass traits were recorded between 2004 and 2012 for 22,620 cows born from 1997 to 2011. The ultrasound measures included backfat thickness (BFT), eye muscle area (EMA), and marbling score (MAR). The mean values for the BFT, EMA and MAR were 4.46 mm, 56.24 cm2, and 4.12 point, respectively. Seven environmental factors, person taking the measurement, region, year of measurement, month of measurement, image interpreter, birth-year and birth-month, were tested to determine if they had a significant effect on the studied traits using the GLM procedure in SAS. All factors were found to significantly affect all the ultrasound carcass traits in this study. Unlike in previous studies, among the environmental effects, the significant effect of the image interpreter on the ultrasound carcass traits was shown for the first time in this study. These results indicate that future genetic evaluations of ultrasound carcass traits of Hanwoo cows should include all of the above environmental factors as well as the effect from people taking the measurements.