Experiments were conducted to evaluate the performance of eight polyhouse cucumber inbreds for earliness, yield and disease tolerance against downy mildew at Bihar Agricultural University, Sabour, Bhagalpur during Spring and Kharif seasons 2018 in saw-toothed naturally ventilated polyhouse. The data were recorded for thirteen quantitative characters viz., days to first female flower anthesis, node number to first female flower, days to first fruit harvest, fruits per plant, flesh thickness (cm), fruit length (cm), fruit diameter (cm), average fruit weight (g), vine length (cm), crop duration, yield per plant (g), TSS and PDI (%) for downy mildew. The study reported that the genotypes BRPCU-1, BRPCU-2 and BRPCU-3 were identified as best genotypes in respect to earliness in pooled over seasons. While, BRPCU-1 and BRPCU-2 showed resistance and moderately resistance, respectively in terms of PDI (%) for downy mildew. For yield and its contributing traits, the inbred lines BRPCU-3 and BRPCU-5 showed better performance in pooled over season.