The aim of this study was to estimate environmental effects on test day milk yield (TDMY) in Patch-faced Maritza sheep breed. Database includes 12 955 milk yield records in the test day. Milk yield recordings were made in 18 flocks and test day milk yields were obtained from 1992 to 2015 (24 years). In the structuring of the database, the following environmental effects were differentiated: animal; flock; year-season of lambing effect (YS); parity effect (Par); litter size at birth (LS); age of ewe at lambing (AgeL); age of ewe at test day (AgeTD); suckling period (Suck); ewe test day (ETD); flock test day (FTD); flock-year-test day (FYTD); stage of lactation period (DIM); stage of lactation period defined at 3-day intervals (DIM3). Average TDMY was 748.59±416.22 mL. The highest test day milk yield was in the first test day of ewes (1015.80±457.67 mL) and gradually decreased to seventh test day (267.50±120.05 mL). All mentioned environmental effects have influence on TDMY and have significant effect (p <0.001). The FYTD had the largest proportion (41.57%) on the total phenotypic variation. A large part of the total phenotypic variation had the following effects: Animal (31.11%), AgeTD (30.95%), DIM (27.85%), DIM3 (27.14%) and ETD (21.92%). Considering the significant influence of the described environmental effects on the TDMY in the population of Patch-faced Maritza sheep breed, they should be taken into account when estimating the genetic parameters.