The Black Widow is a world class athlete, gymnast, acrobat, aerialist capable of numerous complex maneuvers and feats, expert martial artist (including karate, judo, kenpo, jujutsu, ninjutsu, aikido, savate, various styles of kung fu and boxing), marksman and weapons specialist as well as having extensive espionage training.

She is also an accomplished ballerina.

The Black Widow has been enhanced by biotechnology that makes her body resistant to aging and disease and heals at an above human rate;

as well as psychological conditioning that suppresses her memory of true events as opposed to implanted ones of the past without the aid of specially designed system suppressant drugs.

The white blood cells in her body are efficient enough to fight off any microbe, foreign body and others from her body, keeping her healthy and immune to most, if not all infections, diseases and disorders.

Her agility is greater than that of an Olympic gold medalist. She can coordinate her body with balance, flexibility, and dexterity easily.

Romanova has a gifted intellect.

She displays an uncanny affinity for psychological manipulation and can mask her real emotions perfectly. Like Steve Rogers, she possesses the ability to quickly process multiple information streams (such as threat assessment) and rapidly respond to changing tactical situations.

Romanova is an expert tactician. She is a very effective strategist, tactician, and field commander. She has led the Avengers and even S.H.I.E.L.D. on one occasion.

Credit to wikipedia