Passengers departing from Gimpo International Airport in Seoul are weighed in their full attire and with their carry-on bags, Korea Times reported.
But they are free to turn down the request.
An airline spokesman said the data would be kept anonymously and used to calculate the average passenger weight for safety analysis.
In December the airline had weighed some 5,000 passengers on domestic flights. Korean Air had carried out a similar exercise in August last year.