Floristic composition of grasslands is one of the basic indices determining the nutritive value of the sward. It may, however, become simplified or degraded. Direct undersowing may often be sufficient to enrich impoverished sward with special varieties of grasses and legumes. The aim of this study was to assess the effect of meadow sward enrichment through direct undersowing with grass and legume varieties of high nutritive value on the quality of obtained fodder a year after treatment. Static experiment was set up on a meadow of simplified floristic composition in Żuławy Elbląskie situated on alluvial soil. Two weeks before undersowing, weeding was performed by spraying Fernando 225 EC herbicide at a rate of 3 l∙ha-1. The meadow was undersown in the end of September 2012. The assessment of nutritive value of so obtained sward with the RFV index showed that the decisive factors a year after treatment were: application of di- and tetraploid varieties of Lolium perenne and Festulolium brauni and the frequency of mowing. Higher nutritive value was obtained after undersowing with a mixture of seeds with 35% contribution of di- and tetraploid varieties and mowing four times a season. Despite lower dry mass yields per hectare, significantly higher potential milk production was obtained.