Please be aware that Beijing and Seoul has multiple airports and that these results are for all airports serving the city.
The best month to fly between Beijing and Seoul is March and the most expensive month to fly is June. (Average prices, based on 400 datapoints.)
The best day to arrive at Beijing is Wednesday and it would be best to avoid Monday, as prices are on average 52.29% higher than on Wednesday. (Average prices, based on 404 datapoints.)
The cheapest airline flying from Beijing to Seoul is Air China. They are 17% cheaper than Asiana Airlines. (Average prices, based on 404 datapoints.)