YES Anti-freeze is very poisonus for your pet!
Unfortunately both the smell and taste of anti-freeze is generally appealing to pets. Even in small doses the results can be fatal if ingested.
Many cars have some component of anti-freeze in their radiators and unbeknown to pet owners their animals may stop to lick or drink this sweet tasting liquid from a leak or a puddle of inadequately disposed-of fluid. The harmful ingredient in antifreeze is ethylene glycol, an extremely toxic chemical. Even the smallest amount of this liquid can be fatal to a cat or dog.
Symptoms of antifreeze poisoning include a drunken appearance including staggering, lack of co-ordination, and apparent disorientation, vomiting and even seizures.
Take your poisoned animal to the vet as fast as possible. The faster the treatment the better the chances of recovery.