Surgery for patients with lung cancer diminishes their lung functions, due to removal of their lung lobes. Therefore, thoracic surgeons have to consider postoperative lung function of patients. In this review, we explained recent approaches of estimation of postoperative lung function by spirometrical and also pulmonary circulatory measurement values. The most common and simple way to estimate postoperative conditions for patients who undergo lung resections is calculated by numbers of segments that are removed by surgery. However, these methods are not so accurate when the patients have chronic obstructive pulmonary disease. Another method for estimating postoperative conditions using right heart catheterization is a unilateral pulmonary arterial occlusion (UPAO) test. Applying this method, surgery related deaths have been decreased. Since, UPAO test mimics the postoperative state by occluding the pulmonary artery prior to lung surgery, it is supposed to be very accurate. Recently, a novel method to estimate postoperative right heart reserve functions was developed. Using this method, postoperative right heart failures can be anticipated prior to lung resections. In this review, we explain these kinds of methods to prevent impairment of postoperative quality of life.