Seoul to Busan is the route every Korea itinerary eventually needs, and there are really only two sane options: the KTX bullet train or the express bus. I have done both many times — here is how to choose.
KTX: Fast and Easy
The KTX from Seoul Station to Busan Station takes about 2 hours 30 minutes on the direct services. Standard class runs around 59,800 KRW, first class about 83,700. Trains leave every 20–30 minutes from early morning to late evening. Book on the Korail website or the KorailTalk app — English works fine, and you can pick seats. Book a few days ahead for weekends and holidays; Friday afternoon and Sunday evening trains sell out. If you are doing multiple train legs, look at the Korail Pass for foreign tourists, which can undercut individual fares.
Express Bus: Half the Price, Twice the Time
From Seoul Express Bus Terminal (Gyeongbu line, connected to Express Bus Terminal Station on Lines 3/7/9), buses to Busan run constantly — every 15–30 minutes. A standard bus is around 25,000–30,000 KRW and takes about 4 hours 15 minutes in good traffic; the premium "udung" buses with three-across reclining seats run about 38,000–44,000 KRW. Friday afternoons and holiday eves can add an hour or more in traffic. Book at the terminal kiosks (English available) or the bustago/Tmoney GO apps.
Which One?
Take the KTX unless money is genuinely tight — the time saving is worth 30,000 KRW on a short trip. The bus makes sense if you are on a real budget, if KTX is sold out, or if you are traveling overnight (late buses exist; overnight KTX does not). One more option: the slower ITX-Saemaeul and Mugunghwa trains run 28,600–42,600 KRW and take 4.5–5.5 hours — a middle path with a guaranteed seat and a view.
Arrival Notes
KTX arrives at Busan Station, on Line 1 — easy for Jagalchi and Nampo. Buses arrive at Busan Central (Nopo) or Haeundae terminals depending on the service; check which one your ticket uses before booking.