This study aimed to evaluate the effect of different dry period lnghts (DPLs) on the udder health and fertility during the subsequent lactation. The impact of subclinical mastitis (SCM) and clinical mastitis (CM) on the reproductive efficiency were also investigated. Holstein-Friesian cows (n=894) were included in the study of udder health, of which only multiparous cows (n=499) were included in the investigation of the impact of different DPLs on the udder health and reproductive efficacy in the subsequent lactation. Cows were classified according to the DPLs into 3 groups: Short (SDPL, 60 d). A limit of 200,000 somatic cell/mL milk was established to separate between healthy and mastitic udder status. Accordingly, samples with 500,000-1,000,000 cell/ml were referred to cows affected with SCM and samples with >1,000,000 cells/ml were mentioned to cows affected with CM. A higher proportion of infected udder was detected in cows with LDPL (39.19%) Moreover, a higher proportion of SCM was recorded for cows with LDPL (17.57%) compared with that recorded for cows with SDPL (8.0%) and TDPL (6.13%). A higher proportion of CM was recorded for cows with a long dry period (LDP, 8.11%) compared with that recorded for cows with SDPL (4.0%) or with TDPL (4.8%). Cows with SDPL showed the best intervals reproductive indices compared with that recorded for both TDPL and LDPL. Furthermore, LDPL was found to be associated with significantly lower CR (33.11±2.91%), lower PR (50.39±3.97%) and higher NSPC (1.98±0.37) compared with values that recorded for either SDPL or TDPL. Cows with either SCM or CM showed the longest interval reproductive indices, less CR and PR and number of inseminations to become pregnant compared with healthy udder cows. A lower proportion of affected udder was recorded for Primiparous cow (24.3%) compared with that showed by multiparous cows (32.46%). Cows affected with mastitis during the voluntary waiting period (VWP) showed longer intervals to the first detected estrus and first services while those affected during the service period (SP) showed longer calving to conception intervals, lower CR and lower PR especially when the SCC exceed 500,000 cell/ml milk. Cows experienced udder infection during the SP showed the lowest PR (32.54% & 36.44%) and required more NSPC. In conclusion, a significant linkage among different dry period lengths and both the incidence of mastitis and fertility were recorded, with the best results were recorded for cows with TDPL and SDPL. Extending the dry period above 60 days increased the incidence of both clinical and subclinical mastitis and exerted a negative impact on the reproductive performance. The occurrence of mammary infection during the VWP increased the calving to first estrus and first service intervals, while its occurrence during the SP prolonged the days open, and extremely reduced the conception and pregnancy rates.