Abstract: A plurality of blocks, used for a block toy, each of which is formed by mutually connecting unit blocks selected from a first to a 25th unit block, the unit blocks being made by cutting an imaginary base block by four horizontal imaginary cutting planes parallel to each other and four vertical imaginally cutting planes parallel to each other in such a way that each unit block is designated the first to 25th unit block, respectively, arranged from left to right and from top to bottom. In order to build up a structure, a first and a second group of blocks are used in combination.