The one-day meeting at a private members' club in the centre of the Chinese capital is the second round of talks between the South's Wi Sung-Lac and his North Korean counterpart Ri Yong-Ho in two months.
They aim to pave the way for a resumption of full six-party negotiations on the North's nuclear disarmament, a process which began back in 2003 and groups the two Koreas, China, the United States, Japan and Russia.
North Korea formally abandoned the six-nation forum in April 2009, a month before staging a second nuclear test which brought worldwide condemnation and fresh United Nations sanctions.
Now all sides say they want to start talking again, especially after Pyongyang's disclosure last November of a uranium enrichment programme which could give it a second way to make atomic weapons.
But while the North wants six-party talks without preconditions, South Korea and the United States say it must show seriousness about giving up its nuclear arsenal in return for economic, diplomatic and security benefits.
South Korea's Wi, who has said in the past it was "too ambitious" to expect the talks to restart this autumn, said Wednesday's discussions would include the preconditions the North must meet.
"I will discuss a wide range of issues concerning denuclearisation, including the pre-steps," he told AFP during a midday break in the talks.
South Korea's Yonhap news agency said Wi would demand that North Korea stop its uranium enrichment programme before the negotiations could resume, citing a senior Seoul diplomat.
The meeting in Beijing comes after Wi and Ri held surprise talks on the Indonesian island of Bali in July, which were followed by a US-North Korean meeting in New York.
China, which hosts the international forum, expressed hopes Wednesday's meeting would prove fruitful.
"We support dialogue between North and South Korea and we hope the dialogue can produce outcomes so as to promote the six party talks process," foreign ministry spokesman Hong Lei told journalists at a regular briefing.
"We hope relevant parties meet each other half way so as to create the conditions for the early resumption of six-party talks."
But expert Kim Dalchoong said a speedy breakthrough was unlikely.
"The parties won't jump into making decisions to resume six party talks. They will need more rounds of serious discussions," Kim, professor of political science at Seoul's Yonsei University, told AFP in Beijing.