This study aimed to determine the effect of concentrate to forage ratio (C/F) on milk urea nitrogen (MUN), milk production, and reproductive performance of dairy cows of smallholder farmers of Tani Wilis cooperative in Sendang, Tulungagung, Indonesia. A survey was conducted to identify productive cows based on records from the cooperative. Sampling was conducted twice. First sampling was based on reproductive efficiency and milk production criteria. Data on age, parity, postpartum lactation, milk production, reproductive efficiency, body condition score, weight, and feed measurements (forage and concentrates) were obtained from 60 productive cows. Second sampling selected 26 dairy cows with normal estrous cycle. These cows were then allocated into two groups based on their C/F. Their milk and feed were sampled to measure MUN and conduct proximate analysis, respectively. T-test showed that cows that received dietary intake with C/F >30% showed higher (P <0.05) MUN, milk production and reproductive performance than those with C/F <30%.