Disclosed herein are a transformed Synechococcus elongatus strain having improved capability of producing acetone and a method for producing acetone and a method for removing carbon dioxide using the same. In an aspect, the transformed Synechococcus elongatus strain of the present disclosure can produce acetone with high selectivity using carbon dioxide as a carbon source. The present disclosure is economical because the Synechococcus elongatus strain can economically produce high value-added acetone using carbon dioxide existing in the atmosphere as a carbon source without requiring an additional catalytic reaction. Also, the present disclosure is environment-friendly because carbon dioxide in the atmosphere can be removed or reduced using the microorganism.