A sitting device for prevention of spinal diseases comprises a padded member, a thin pad extended forwardly from the padded member, and a hard block fully inserted inside the padded member. The padded member has a generally hexagonal shape, and is made of resilient materials. The hypotenuse surface of the padded member is undulating economically. The hard block is made of a non-resilient material, and is able to tolerate, without rupturing, the gravity force on a mass of an adult's body with a shape and size similar to those of the adult's buttocks. The hard block is inserted completely inside the right angle area of the padded member. The height of the front side of the hard block is greater than the distance from the lowest point of the sitter's coccyx to the lowest point of his tuberosity of the sacrum. This will always keep the sacrum in a position higher than that of two seating areas keeping the pelvis upright and symmetric. Both the padded member and the hard block have a flat bottom side to ensure stability.
