Objective To determine the efficacy of forced expiratory volume in six seconds( FEV6 ) as an alternative for forced vital capacity( FVC) in the diagnosis for mild-moderate chronic obstructive pulmonary disease( COPD) .Methods A total of 402 mild-moderate COPD and 217 non-COPD patients’ spirometric examinations were retrospectively analyzed. The correlation between FEV6 and FVC, FEV1 /FVC and FEV1 /FEV6 was evaluated by the Spearman test. Considering FEV1 /FVC lt;70% as being the ‘golden standard’ for airway obstruction, a ROC curve was used to determine the best cut-off point for the FEV1 /FEV6 ratio in the diagnosis for COPD. Results The Spearman correlation test revealed the FEV1 and FEV6 , FEV1 /FEV6 and FEV1 /FVC ratios were highly correlated ( r = 0. 992, 0. 980, respectively, P = 0. 000) . Using FEV1 /FEV6 lt; 70% as the diagnosis standard, 12. 69% of the 402 patients could not be diagnosed as COPD. The FEV1 /FVC ratio of these patients was very close to 70% . The best cut-off point for the FEV1 /FEV6 ratio in the diagnosis of mild-moderate COPD was 72% while the sensitivity and specificity were 94. 7% and 92. 2% , respectively. Conclusions There is a b correlation between FEV1 /FVC and FEV1 /FEV6 . The FEV6 can be a valid alternative for FVC in the diagnosis for mild-moderate COPD, although it may result in false negative. The best cut-off point for the FEV1 /FEV6 ratio is 72% .