A simple apparatus consisting of a plastic syringe coupled with a U-tube has been constructed. This setup is filled with water to trap air in one arm of the U-tube. A change in the volume of the enclosed air causes a change in its pressure that is indicated by the difference in the water levels. Boyle's law is shown by a linear relation between the pressure and the invers of the volume observed in the experimental result. Using the best linear fit we obtain the atmospheric pressure to be (108.7 ± 4.5) kPa.