West Australian One Nation senator Rodney Culleton has had another battle with the justice system, this time over his attempt to sue 18 people for defamation.

Last week, Senator Culleton failed in his bid to stop creditors pursuing him for $280,000 over a failed property deal, in what the judge described as an "unusual" matter.

Now, in an unrelated case, he has been refused leave to amend a defamation writ Justice Kenneth Martin described as "incoherent".

Senator Culleton filed the writ in March this year naming 18 people as defendants in his defamation claim for $250,000 in damages.

The claim refers to comments posted on an "Australian Sixty Minutes Programme of Channel 9 Face Book (sic) Account" following a program about farm foreclosures which heavily featured the former farmer.

Senator Culleton was ordered to file proposed amendments to deal with the writ's 'deficiencies' but Justice Martin noted he had sought to add extra defamatory publications beyond his original grievance.

The new proposed writ, filed in July, claimed the 18 defendants published comments primarily on Facebook "in or around April 2015 to August 2015".

"The plaintiff is a public figure and has incurred ridicule and has been gravely injured in his credit, character and reputation," it read.

"He has been brought into public hatred, scandal, odium and contempt and has been lowered in the estimation of the right-thinking members of the community."

But the proposed amendments include at least eight alleged defamatory publications on dates other than those stated in the original document, and on pages unrelated to 60 Minutes.

One of the damages claims related to comments allegedly posted by Rebecca Ford on the GWN7 Facebook page, which read, "Oh Chris, if only they knew moe [sic] about this man".

In his judgement published on Friday, Justice Martin said an "allegedly pejorative imputation ... out of the bland words of that rather brief post, have not yet been formulated by the plaintiff".

"The words 'knew mo[r]e' raising the obvious question: knew more about what? Probably not, I infer, 'more' about the plaintiff's fishing, farming or dancing exploits," he said.

Justice Martin ruled that given several of the publications to be complained about were not contained in the original writ, leave would be needed to change the application.

He refused to grant leave to amend the writ at this stage and will hold a short hearing with both parties to consider alternatives next week.