You do have to report the sale on your tax return. Whether it will be taxable depends on whether you have a gain or a loss. If you have a gain it will be taxable income. Whether you have a gain or a loss depends on your basis and how much you sold it for. To calculate your basis see the link that M-MTax posted above.
You didn't say what the property is. There might be an exception if it's a home that you lived in as your main home for part or all of the 5 years preceding the sale.
You also didn't say whether the other owners will sell their shares of the property at the same time, and whether they also received their shares as gifts.
There might also be special considerations if you sold your share to a relative.
Because of the complications of having multiple owners, having received your share of the property as a gift, and other possible complications, you should consult a local tax professional who can review all the details of the sale and advise you about the tax considerations.
