This study was carried out to estimate environmental effects such as calving season, calving year on peak milk yield, days in milk at peak production(PKD), drying-off milk yield on 305-day, 305D milk yield, and persistency. The data used in this study were milk yield records from first freshened Holstein cows(187 heads) bred in National Livestock Research Institute from 1990 to 1996. Calving season, sire and calving year didn`t affect days in milk at peak(PKD). But peak milk yield(PKM) was significantly affected by calving season(p$lt;.01) and calving year(p$lt;.05). Calving season, sire and calving year significantly affected the drying-off milk yield at 305D(DRYM) related to persistency(p$lt;.05). The PKD was 58.2±23.2day, peak milk yield was 26.2±3.9㎏ and drying-off milk yield on 305-day was 15.7±3.5㎏. The persistency showed 60.3 13.8%, and the phenotypic correlations of persistency between PKD and DRYM was positive.