More than half of the animals were killed in the Kruger National Park with the rate of the slaughter likely to mean that the year's final tally will pass last year's carnage of 448 animals poached.
The department of environmental affairs said: "The latest rhino poaching statistics indicate that a total of 381 rhino have been killed since the beginning of this year."
With roughly 20 000 rhino, South Africa is home to nearly 80% of the world population.
But there has been a devastating increase in poaching in recent years as black market demand for rhino horn has grown with numbers leaping from 13 in 2007 to 333 in 2010.
Heightened security measures have failed to stop the criminal syndicates that officials say are responsible for the killing.
The animals' distinctive horns are hacked off to be smuggled to the lucrative Asian black market, where the fingernail-like substance is falsely believed to have powerful healing properties.
On the black market, the horns are worth their weight in gold.
Soldiers and specialist investigators have been deployed to national parks to battle the poachers.
Despite the rise in the numbers of killings since July, the number of arrests has slightly gone up to 199 from 176 suspects held two months ago.