Potato (Solanum tuberosum L.) is an important cash and food crop in Ethiopia. However, the yield of the crop is constrained by a number of factors. Among the constraints, the use of inappropriate seed tuber size and limited availability of improved varieties are the main ones. A field experiment was conducted to evaluate the effect of different tuber sizes on the growth and yield of potato varieties and to determine optimum seed tuber size for economical feasible production of potatoes during the 2022 irrigation season in Banja district. The treatments consisted of four potato varieties (Belete, Burka, Jalene and Local (Key Dinch) and three seed tuber sizes: small (25-38g), medium (39-75g) and large (>75g). The experiment was laid out in a Randomized Complete Block Design with three replications in factorial arrangement. The collected data on phenology, growth, yield and quality related parameters were analyzed using SAS (Version 9.4) software. The results showed that varieties and seed tuber size in their main effects significantly influenced days to 50% emergence, days to 50% flowering, main stem number per plant, average tuber number per plant, average tuber weight per plant, yield of very small, small and medium sized tubers, unmarketable tuber yield, specific gravity and dry matter content. The interaction effect of seed tuber size and variety significantly influenced days to 90% maturity, plant height, large sized tuber yield, marketable tuber yield and total tuber yields. Concerning the improved varieties used in the present study performed well in almost all the tested parameters of potatoes compared to the local variety but local variety matured earlier as compared to improved variety which is related to early emergence and flowering. The highest marketable tuber yield (41.75 t ha -1 ) was recorded from the large tuber sizes of Belete variety, while the lowest marketable tuber yield (11.40 t ha ) was obtained from a local variety which was planted using a smaller seed tuber size. Based on the partial budget analysis of the present study, Belete with large tuber size gave the highest net benefit of 683208.06 Birr ha -1 with an acceptable level of MRR value of 679.59% for resource-full farmers. However, Belete with small seed tuber size with a good net benefit of 471835.39 Birr ha−1 and highest acceptable level of MRR of 3783.27% are for resourcepoor farmers, can be recommended for economical production of ware potatoes in the study areas. As the results are limited to one season and location, further study over seasons and locations is recommended in order to generate a more reliable and sustainable result. -1