The role of the oxygen content in influencing the structure and physical properties of double layered manganites La 2 - 2 x Sr 1 + 2 x Mn 2 O 7 + δ with x~0.5, has been investigated by means of X-ray diffraction, resistivity and magnetization measurements. The variation in the oxygen content causes the same physical effect as the Sr concentration, leading to a change in carrier density. In particular, the magnetic behavior seems to be influenced more with a change of the oxygen content than by that of Sr concentration. We will display the oxygen content-dependence on the magnetic and transport properties and discuss the role of the oxygen content in the double layered manganites with x~0.5.