It is planned to increase plant biomass feedstock to sustain the renewable energy source, bioenergy. In cool regions such as Hokkaido which often offers a short and stressful growth season, less is known about biomass potential (BP) in plants, and generally there is a lack of data regarding a regional suitable harvesting system in feedstock. A constant supply of feedstock per month using several biomass plants would be important for establishing an all year round operating system (AYROS) in biofuel production. Two types of perennial lignocellulosic crops, four C3 grasses which adapt well to cool environments, orchardgrass (OG), reed canarygrass (RC), tall fescue (TF) and timothy (TI), referred to as cool season grasses (CSG) and C4 native grass, Miscanthus sinensis called 'susuki', were evaluated for the BP in Sapporo, Japan. CSG were sown into fertilized land in 2006, whilst M. sinensis was planted in 2007 without fertilization. Three years after planting, in 2009, regional potential across all harvesting of CSG was 9.7 t ha-1 year-1. Different harvestings of CSG revealed high BP from RC and TI rather than OG and TF. RC showed BP peaks twice, in June (11±0.45 t ha-1 year-1) and September (15±1.11 t ha-1 year-1), and a single peak in July (15±1.99 t ha-1 year-1) for TI, indicating that RC is a two peaks type, whilst TI falls into a one peak type. For M. sinensis, the BP increased with the year and varied among accessions. In 2009, regional potential was 1,287±343 g plant-1 year-1. Accessions native to Hokkaido showed maximum BP of 827±353 g plant-1 year-1, mainly from Matsumae (1,622±692 g plant-1 year-1) and Toyoura (2,174±169 g plant-1 year-1). Accessions native to areas other than Hokkaido yielded a potential of 2,206±388 g plant-1 year-1, mainly from Shiozuka (2,531±526 g plant-1 year-1) and Akeno (2,653±635 g plant-1 year-1), substantially higher than the BP of Hokkaido accessions. The BP of M. sinensis over two years of 9 accessions in the present study was about 36.9 t ha-1 year-1, by converting biomass data of plant (921.4 g plant-1 year-1) to land area unit. The BP experiment estimates biomass feedstock is supplied with 10-15 t ha-1 by harvesting TI and RC in June to September and 30 t ha-1 by harvesting M. sinensis in October. This study demonstrated the feasibility and advantage of the combination of CSG and M. sinensis. The BP could be improved using mostly superior genotypes of M. sinensis selected from areas other than Hokkaido. The information from the present study will be available for establishing AYROS in feedstock production for biofuels such as bioethanol in cool regions such as Hokkaido.