The guard dog fell ill on January 8 after eating pellets thrown over a fence into Third Energy's site in Kirby Misperton, near Malton.
It was taken to a vet for treatment after eating some of the pellets and then vomiting and collapsing.
Several pellets were seized from the site which North Yorkshire Police earlier said were suspected to be aniseed balls.
Officers searched a nearby caravan as part of the investigation, before arresting two men in connection with the suspected poisoning.
But the force said last night that it would not be bringing charges against the men, aged 42 and 61.
A spokesman said: "Two men arrested following an incident in which a guard dog became ill at Kirby Misperton will face no further action.
"Due to insufficient evidence, no further police action will be taken in relation to the incident."
He added that the dog made a full recovery since the incident.