A quantitative trait was affected directly or indirectly by several factors due to relationships among them. It is necessary to identified direct and indirect effects of a factor to reveal all relationships in a detailed way. In this study, total of 11647 305-day milk yield records from the 7 parities of 5047 Holstein Friesian cows were statistically evaluated for determining direct and indirect effects of parity (X1), year of calving (X2) and lactation length (X3) on 305-day milk production (Y) via path analysis. Correlations among 305 day milk yield, parity, year of calving and lactation length were calculated 0.17, 0.43, 0.54 respectively and found statistically significant ((P<0.01). The direct effects of the parity, year of calving and lactation length on 305-day milk production were found PY1=0.12, P21=0.10, P31=0.46 respectively and statistically significant (P<0.01). The indirect U effect of parity via year of calving and S effect via lactation length on 305 day milk yield were found 0.01 and 0.04, respectively. The indirect U effect of year of calving via lactation length and S effect via parity on 305 day milk yield were found 0.31 and 0.02, respectively. Moreover, the indirect U effect of lactation length via year of calving and S effect via parity were found 0.07 and 0.01, respectively and lower.