Abstract: A seat of a chair is provided with a plastic main body, a metallic upper cover joined to upper and annular sides of the main body, and a metallic lower cover securely disposed over the bottom of the main body. The metallic covers increase the strength of the seat. The bottom of the plastic main body is formed with vertical connecting tubes, which are tightly fitted around corresponding sleeves secured to upper ends of metallic legs of the chair. The tubes have inner annular protrusions, which are engaged with annular grooves formed on outer sides of the sleeves; and, the seat matches the metallic legs to a greater degree because the outer side of the seat is made of metal.