High Kick! The Revenge of the Short Legged 123 eps.
A Daughter Just Like You - 120 episodes 
Five Children (54 ep)
Dong Yi - 60 episodes 
MONSTER (50)
LEE SOON SHIN (50)

For Korean.... its Six Flying Dragons - 50 Episodes
Monster (50 episodes)

I'm now watching What Happens to My Family? (53 episodes)
King's Daughter Soo Baek Hyang, 108 episodes.

However, since those are 1/2 hour episodes, the actual longest series I've watched in terms of length is Queen Seon Deok, though not by a whole lot.
Six Flying Dragons 50 Eps 
Can You Hear My Heart 30 episodes...I don't have time for anything that is longer than 30 especially with Kdramas being an hour or so long lol 
Ugly Alert, 133 episodes :)
20 episodes is my limit. I have commitment issues lol.
Stairway to Heaven, 121 eps