An automatic chainsaw chain tension adjuster is provided. The automatic chainsaw chain tension adjuster maintains the chain of a chainsaw on the chainsaw guide bar during use. As heat expands the overall length of the chain while the chainsaw is running, an internal spring forces a sprocket located at the second end of the guide bar outward therein increasing the overall path the chain must travel around the guide bar/sprocket to compensate for the heat expansion. As the chain of the chainsaw heats up or cools down during use and non-use, the internal spring automatically adjusts the chain to the exact proper tension.