I am redesigning a website for a client.

He has some pages set up which perform reasonably well but the urls consist of keywords seperated by %20.

Would it best to replace the %20, or does this not bother google?

I think as long as the url is not the type of full-keyword thing, Google won't see your site as a spammer. It depends on how you optimizes that certain website..

I feel like it'll be fine... just dont over-use the keyword in the site content.

(i would personally delete the 20% though, (assuming you are implying that it is physically in the url)

It is actually a space that is in the url

yes actually a space that is in url.

It seems to me that everything will be fine ... Not only the abuse of the keywords the content of your site.

I don't think in this case there is an abuse of keywords, although I have seen this done in other sites. There are 3 keywords or should I say one 3 word keyphrase used in the url and it sums up the content of the page and the site in general.

Thanks everyone for your help

Yes, replacing the spaces with a dash is what I want to do.

My concern is that the page as it is has a high pagerank and I am worried that replacing the spaces with dashes might harm this.

Yes you must consider it with your client before making any changes in your site