This paper deals with the existence of solutions of the periodic boundary value problem of the impulsive Duffing equations: x ′ ′ ( t ) + α x ′ ( t ) + β x ( t ) = f ( t , x ( t ) , x ( α 1 ( t ) ) , … , x ( α n ( t ) ) ) ,   a.e.     t ∈ [ 0 , T ] ,   Δ x ( t k ) = I k ( x ( t k ) , x ′ ( t k ) ) ,   k = 1 , … , m ,   Δ x ′ ( t k ) = J k ( x ( t k ) , x ′ ( t k ) ) ,   k = 1 , … , m ,   x ( i ) ( 0 ) = x ( i ) ( T ) ,   i = 0 , 1 . Sufficient conditions are established for the existence of at least one solution of above-mentioned boundary value problem. Our method is based upon Schaeffer's fixed-point theorem. Examples are presented to illustrate the efficiency of the obtained results.