Purpose: This study investigated the harvesting properties of the giant miscanthus (Miscanthus ${ imes}$ giganteus) to measure the required mowing power for different stem conditioning methods in order to shorten the drying time after mowing and the bale density so that the crop can be used as biomass in the winter season. Methods: The required mowing power and bale density were measured using a power measurement device, three different mower-conditioners, and a mid-sized round baler under different working speeds and conditioning methods. Results: For the various mower-conditioners, the average stem length from mowing was 0.86-0.91 m, and the available working speed was 1.6 m/s. The steel roller-type mower-conditioner showed better stem conditioning but could not mow over a working speed of 1.6 m/s. The required average power of the mower-conditioners varied from 23.8 kW for the steel roller-type rotary disk mower-conditioner with a working width of 2.4 m to 37.2 kW for the flail-type rotary disk mower-conditioner with a working width of 3.2 m at a working speed of 1.6 m/s. The bale densities were $155.8-172.2kg/m^3$. The highest bale density was measured for stems with no conditioning and a moisture content of 11.3% (d.b.) mowed by the rotary disk mower. The bale density was affected by the mowing method because of the low moisture content of the miscanthus stems. Conclusions: In terms of the working performance and conditioning statue, the steel roller-type mower-conditioner is a better choice at a working width of 2.4 m, while the flail finger-type mower-conditioner is better at a working width of 3.2 m. The type of mower-conditioner used for giant miscanthus harvesting should be determined by considering the harvest area, workable period, and working performance of a mower-conditioner and baler during the winter.