The man, who had significant pre-existing underlying health conditions, died earlier on Thursday evening in Edinburgh Royal Infirmary.
The health board said that he was one of the confirmed cases in the outbreak, which began in the Scottish capital at the beginning of June.
The first man to die was named as Robert Air, 56, from the Seafield area of the capital, whose death was reported on June 5.
The Scottish Health Secretary says there are 24 confirmed and 37 suspected cases of Legionnaires' disease. She expects this figure to rise.
Legionnaires' is a disease that strikes fear in people and its history shows it can be deadly.
The Scottish Health Secretary will today update MSPs on efforts to deal with a deadly outbreak of Legionnaires' disease in Edinburgh.