To provide a block toy capable of assisting the development of thinking power in the intellectual training field of infants by making a block toy able to be assembled in all directions without limiting the attaching surface of the block toy.

The attaching grooves 6 of a block are formed on three layers including a base layer, a receiving layer and a claw layer and the four blocks form one set. Upon attaching one block to another block, the claws of the attaching grooves 6 of another block are fitted to the receiving grooves of claws. A surface of one block which is desired to engage with the surface of another block faces the surface on the basis of this principle and one block is merely rotated by 45° in the direction shown by an arrow, so that one block is attached to another block. When the one block is rotated by 45° in the opposite direction, it is detached from the other block. Since the block is made of polyethylene, it can be easily worked and is light. Further, the block has a slight flexibility so that a distortion may be generated without a trouble upon attaching and detaching the block.