The objective of this study was to estimate the effect of age of Czech Fleckvieh heifers at first service on their reproduction and milk performance. There were observed reproduction parameters of 2019 heifers and cows at first to third calving interval in four farms. Milk production parameters were observed at first, second and third lactation of cows. Analyses were carried out using the GLM procedure (linear model with fixed effects) in programme SAS 9.1. The results showed that lower age of heifers at first service do not have negative effect on their further reproduction and positively affects their milk performance. In terms of overall reproduction efficiency and whole life milk performance is possible to recommend the age of Czech Fleckvieh heifers up to 501 days as a suitable age for first service.