I think I'm in big trouble. I bought an apartment in joint name with my husband 5 years ago and we've leased it to the same guy for the whole time. Now he wants to move and I'm looking for a new tenant. The real estate agent says that we need to produce a "Certificate of Real Estate Ownership" (fangchang zheng) in order to sign a contract with a new tenant. Well, I don't ever recall having such a certificate. And we certainly did not show the certificate to our old tenant when we signed our contract 5 years ago.

I know it may sound like a silly question, but does anyone have any idea where it might be??? Would our lawyer or mortgage provider or even the developer have a copy? Or were we never given a copy because we are foreigners? Assuming I've lost it, does anyone know where can I get a new copy?

Its not a certificate, its the green book that proves you own the apt.
If you don't have that, yes, you really are screwed.

You should have that in a safe place.
As well as the piece of paper (usually stapled to the book) which allows you to change the pin/password.

If you don't, then suggest go to the local district housing office, and enquire about whether your apt is still in your name, and how to get another book.

I haven't needed to show one to agents to lease before, but really depends on the agency.