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?

You should pay a visit to the property tax dept in your district asap to sort it out. If you didn't pay the neccessary taxes when purchasing your property, you won't received this cert. No cert, no rent. Because the tenants will not be able to tell if you're a scam landlord without the cert.

Why did you double-post???
It also has to do with the Developer.
For your sake I hope the property was approved and licensed by the gov't. Several were just land takeovers and officials got kickbacks, they never owned the property so could not 'sell' apartments legally or provide the certification docs.