This study was conducted to estimate variance components, genetic parameters and breeding values of 298 Brown Swiss cows milk yield recorded between 1987 to 1999. Estimates of variance components, genetic parameters and estimates of breeding values of 305-day milk yield were obtained for each of animals using two different models. First lactation records were analysed in a model (Model 1) that included direct genetic effect as the only random factor. All lactation records were analysed in a model (Model 2) that was the same as Model 1 but permanent environmental effects associated with animal were also taken into account. The heritability of milk yield for first lactation and all lactations were 0.23 and 0.19 respectively. According to analyses among the years, there was no any constant trend for phenotypic and genetic values of 305 day milk yield. Generally an irregular fluctuation was observed. This irregular fluctuation may demonstrate that there was no any standard selection programme in the herd.