It's really rare for the government to take action like this - it hasn't banned a toy from being sold for over 10 years.
It stopped jelly balls from being sold in 1992 because the squidgy toys broke into pieces and could be swallowed.
And in 1991 scented rubbers were banned because some kids tried to eat them.
The Yo-Balls are made of a squidgy ball filled with liquid attached to a piece of elastic with a small finger loop at the end.
They're really stretchy and can get tangled round your necks when you swing them round your head.
'Throw them away'
The government has tested them and found they could actually strangle someone.
It's now asking people who've already got the Yo-Balls to throw them away.
The government said: "It is clear this toy poses a very serious risk to children. I do not want to spoil the fun that sensible use of the toy can bring, but I cannot ignore children's safety."
From now on, companies and shops won't be able to sell the toy and will be breaking the law if they do.
One of the companies which supplied the toy said:
"H. Grossman Ltd. voluntarily withdrew their version of the Yo Ball at the beginning of April.
Subsequently Trading Standards visited other manufacturers of Yo Balls and advised them to do the same. After deliberation it has now been announced that the DTI has banned the sale of all Yo Balls."