I inherited properties in forigne country since I was ten years old.since then these properties have become valuable.if I am to liquidate and bring the cash to the US.Wili I be liable for capital gain taxes?I am a us citizen now but all my inheritance has been in my name way before I became a citizen.

As a U.S. citizen, ALL world-wide income is subject to U.S. income tax, so, ys, you WILL be liable for capital gains on the difference in value between when you inherited the property and the price you receive when you sell it.