The experiment was conducted in order to clarify influences of outdoor air supplied through openings on thermal environment in rooms heated by floor heating systems. The ari supply openings of various heights and types were used in respective experiment cases. The following results were obtained: (1) Draught Rating (DR) was increased by sypplied outdoor air in any heights of air supply openings and openings with natural ventilation systems. The DR in areas near the air supply openings were higher than DR in far area. (2) Influences of outdoor air supplied through openings in the heights of more than 1600mm above floor were small on thermal environment. (3) The air supply openings with mechanical ventilaion systems made better thermal temperature than openings with natural ventilation systems because mechanical ventilaion systems controled temperatures of supply air.