My father passed away in 2003. I want to be included as an heir to his property. I'm 54 but my sister state that I;m not part of the estate because I am a child out of wed lock. Can I poceed to verify I am his child

If he died in 2003, then its probable that a) his property has already been distributed and b) the statute of limitations for filing a claim against the estate has long past.

Also you don't say whether he had a will. If he had a will and you were not included and he was aware of you, that also limits your chances of getting anything out of the estate, if there is anything left to get.

If you want to establish a biological connection to him, you can have a DNA comparison done with your siblings. That may be able to show that he was your father. But, frankly I wouldn't waste the time, since, even if you can establish a biological connection, the other factors will probably make it moot.

Where exactly would this be? In many places just being a child doesn't entitle you to a chunk of an estate... the parent could give everything away and leave nothing to the children... or even completely ignore certain children. But as Scott stated...he died a very long time ago 11 years to be precise...its unlikely you would ever see anything because its already gone to where it was intended...either by will or probate.

As has been noted, we need to know what state or country this is. But in many places, a child of a decedent doesn't have to be a legitimate child in order to inherit. If it is in one of those places, the sister would be incorrect.

We are waiting for OP to tell us, but I am guessing that the estate was never probated and there was no will.