Yes they are poisonous and yes it is fine to compost them as no-one is going to eat them and, once composted, they are not toxic.

I've been putting mine in the compost bin for years, and last time I checked, I was still alive :-)

Rhubarb leaves are toxic when alive and contain whats known as "OXALIC ACID"
rhubarb leaves if eaten will "NOT" kill you but will cause you tobe sick.

Once rotted they are then non toxic so its safe to use on the compost.

Ive used "tried & tested all the above for many years.
But if you want the full rhubarb safe check google ruhbarb and its all there for your peace of mind.

Thanks again, that's reassuring to know.

'rhubarb leaves if eaten will "NOT" kill you'

Try telling that to the people who died after eating them. There are case studies in the literature. Some of them question whether it is the oxalic acid that makes it lethal as concentrations don't seem to be high enough.

Aren't rhubarb leaves supposed to deter a pest if buried around the roots of the plant? Or does it cure clubroot, or something? I can't remember, but I expect someone else on GOY will know!!