Although age of air measurement has been carried out frequently in order to evaluate various ventilation systems, it is pointed out that the measurement term is relatively long, and that changes of outdoor and indoor climate often affect the measured results. In this paper, simple measurement method for age of air assuming uniform mixture model is tried, and verified by existing houses experiments and case study with mathematical multizone infiltration model. The results are as follows. (1)As a result of measurement for three highly insulated houses, root mean square error of age of air between simple and detailed method is about 25minutes. (2)This simple method may be applied to following conditions, a) indoor partition is not air tightened and b) nominal ventilation time is less than analysis term (2h, in this paper). These condition is not inconsistent with the measurement for ordinary highly insulated houses designed to the ach index to be 0.5.