By planeThai AirAsia flies from Bangkok (DMK) to Khon Kaen (KKC) several times a day; there are also flights from/to Chiang Mai(CNX), Pattaya (UTP) and Phuket(HKT). Nok Air and Thai Lion Air each has a couple of flights a day to Bangkok (DMK) as well. Thai Smile Airways flies from Bangkok (BKK) five times a day, and can be booked in one ticket with an international Thai Airways flight.
By trainKhon Kaen is on the branch of the Northeastern Line that runs to Nong Khai and Laos. The State Railway of Thailand (SRT) runs one reasonably timed overnight train, Train 133, which leaves Bangkok at 20:45 and is scheduled to arrive at 06:11 in Khon Kaen.
By busUntil 1 December 2017 Khon Kaen had three bus terminals. The newest, Terminal 3, is eight kilometres out of town and, for that reason, inconvenient. The city fathers want to get buses out of the city's core. The taxi cartel supports that initiative for obvious reasons: the cost of a tuk-tuk or taxi to downtown may well cost more than your bus ticket to Khon Kaen.
By carIt's easy to get to Khon Kaen by car from Bangkok. Just follow the four lane Hwy 2. Hwy 2 also heads north to Udon Thani, Nong Khai, and Laos.