The main purpose of this study is to develop a design fire for parking lots structured by steel which is applicable to fire protection. First of all, the amount of combustible materials used in motorbikes was investigated. And then, two series of full-scale burning tests were carried out to reveal the burning behavior as free burning. The first series of full-scale experiment was conducted to realize the single motorbike burning characteristics, for instance heat release rate (HRR), flame height and temperature. In this series, each of twelve motorbikes which are different from the engine displacement and type was burned. The engine displacement were grouped into 4 sizes (50cc, 250cc, 400cc, 750cc), and the motorbike types were classified into 3 categories (road type, sport type and scooter type). Experimental results indicated that the maximum HRR changed by depending on combustible surface area, and an amount of combustible was depended on motorbike type, not displacement. In the case of a scooter type, the 20% of the total initial weight was combustible part. The maximum HRR of a scooter type 50cc motorbike was 1.4 MW and an average flame height was 2.6 m, and the HRR of a scooter type 250cc motorbike reached 5 MW and the height exceeded 3 m. In the other series, two motorbikes (scooter type 50cc x 2) were put, which offset distance is 1m, and one motorbike was ignited. Non-ignited motorbike received heat flux from the burning motorbike, and side plastic parts were ignited at t=525 s. The side parts burned speedily and HRR of non-ignited motorbike increased rapidly because of a pyrolysis development. The maximum HRR of non-ignited motorbike was greater than that of single motorbike.