There is a monsoon season that occurs from late June to mid-July, otherwise Korea has 4 seasons: Spring (middle of March to the end of May); Summer (June to August); Autumn (September to November) and Winter (Dec to middle of March).

 Korea have cold and dry winter, and hot and wet summer. Raining season(Jangma) starts in middle~end of June and ends in middle~end of July, so visiting Korea in this season is not wise. In spring and fall the weather is pretty good, so it is the best time to visit Korea. Also if you can stand cold weather winter may be an option. Snow can be an obstacle, but since winter is dry in korea there aren't much snowing day in Korea. But like most nations, summer is not a good season for travelling.

Monthly and seasonal weather averages for Seoul weather provided by the Korean Meterological Administration and up to the minute weather at Gimp'o and Incheon Airports are available.