Yes,
however in order to be able to use it as a deduction you should make sure to
donate it to a 501C-3 Non-Profit organization and you can receive a receipt for
it. Also, it will only be deductible if
you itemize your deductions, if you use standard deductions on your return you
will not be able to include the car seat.
To learn more, please see Turbo Tax short article on the topic at Tax
Deductions and Charitable Contributions.