Can you claim your x wife as dependent on taxes?

Yes, you can. If she has no taxable income and actually LIVES IN YOUR HOME for the WHOLE tax year, she is considered a dependant. Most people think that dependants are children, but there is actually no age limit to a dependant. One other example would be if you had an elderly parent come to live with you in their last years. Same difference (and, maybe someone you love a little more than an ex-wife).