The bombing occurred in the town of Spin Boldak in Kandahar province near the Pakistani border, the Nato-led International Security Assistance Force (ISAF) said in a statement on Friday.
The Nato force has now lost 10 soldiers to hostile action since taking control of the dangerous south of the country on July 31 from a US-led force that overthrew the Taliban in 2001.
"Today an ISAF soldier died in Kandahar province following a vehicle-borne suicide bomb attack," the statement said.
"The incident occurred on the road from Spin Boldak to Kandahar, when a white Toyota Corolla drove towards an ISAF convoy, and exploded near one of the vehicles," it added.
The soldier's nationality would be released by the relevant country.
Abdul Wassay Alokozai, a local police chief, said it appeared to be a suicide blast and added that Nato troops had sealed off the area.
Self-proclaimed Taliban spokesman Yousuf Ahamdi said by telephone from an unknown location that the attack was a suicide bombing carried out by a Taliban fighter.
"The suicide bomber was an Afghan and his name was Ilhas," he said.