An office chair comprising: - a base having a telescopic post; - a backrest and a seat which are rigid elements; said rigid elements being coupled mutually with a hinge; - a synchronized mechanism which is fixed on the telescopic post of said base and supports said backrest and said seat, which are rendered interdependent by said synchronized mechanism; - a single flexible covering element, made from net, from fabric or other suitable material; wherein said single flexible covering element extends from the backrest to the seat without discontinuities; said office chair being characterized in that: - the seating space of the chair is entirely defined by a single curved line which is obtained by joining said rigid elements which are coupled mutually with said hinge, along a horizontal axis perpendicular to the longitudinal centerline plane of the seating space; - the seating surface of the seating space is obtained from said single flexible element, which is affixed to said curved line that defines and delimits the seating space; - said hinge is adjacent to the overlying flexible covering element in order to contain the stretching of the single flexible covering element when reclining the backrest; - two mirror-symmetrical portions protrude forward, in a front region, from the rigid element that defines the backrest, which is pivoted on a rotatable joint in the synchronized mechanism and elastically countered at a point, and said two mirror-symmetrical portions are contoured and adapted for hinging by way of the hinge of the rigid element that defines the seat; - the rigid element that defines the seat, which is coupled in a front region to the underlying synchronized mechanism by two first bushings which are hinged in the rigid element that defines the seat and by two second bushings which are integral with the first bushings and are hinged to the sides of the synchronized mechanism, has two mirror-symmetrical arms (B 1) which protrude rearward, in a rear region, for a rotatable coupling thereof to the two mirror-symmetrical portions of the rigid structure by way of the hinges, thus completing the curved line of the seating space. - a base having a telescopic post; - a backrest and a seat which are rigid elements; said rigid elements being coupled mutually with a hinge; - a synchronized mechanism which is fixed on the telescopic post of said base and supports said backrest and said seat, which are rendered interdependent by said synchronized mechanism; - a single flexible covering element, made from net, from fabric or other suitable material; wherein said single flexible covering element extends from the backrest to the seat without discontinuities; - the seating space of the chair is entirely defined by a single curved line which is obtained by joining said rigid elements which are coupled mutually with said hinge, along a horizontal axis perpendicular to the longitudinal centerline plane of the seating space; - the seating surface of the seating space is obtained from said single flexible element, which is affixed to said curved line that defines and delimits the seating space; - said hinge is adjacent to the overlying flexible covering element in order to contain the stretching of the single flexible covering element when reclining the backrest; - two mirror-symmetrical portions protrude forward, in a front region, from the rigid element that defines the backrest, which is pivoted on a rotatable joint in the synchronized mechanism and elastically countered at a point, and said two mirror-symmetrical portions are contoured and adapted for hinging by way of the hinge of the rigid element that defines the seat; - the rigid element that defines the seat, which is coupled in a front region to the underlying synchronized mechanism by two first bushings which are hinged in the rigid element that defines the seat and by two second bushings which are integral with the first bushings and are hinged to the sides of the synchronized mechanism, has two mirror-symmetrical arms (B 1) which protrude rearward, in a rear region, for a rotatable coupling thereof to the two mirror-symmetrical portions of the rigid structure by way of the hinges, thus completing the curved line of the seating space.