Positron lifetime spectroscopy is a reasonably accurate method to study defects in materials.In this method the time difference between emission of the 1.274 MeV gamma-ray (which is emitted Simultaneouswith positron from a 22 Na source) and the 0.511 MeV gamma-ray (which is emitted as a result of positron annihilation in the sample surrounding the source) is measured. This time difference is the positron lifetime in the sample which is directly related to the size and the number of defects in the sample in which the positron has been annihilated. In addition, the structure of defects in a metal sample is changed with annealing temperature and this effect can also be investigated by positron lifetime measurement. In this work, reasonably good time resolving power was first determined for the system using a 60 Co source and then a 22 Na source was placed between two copper samples and positron lifetime was measured at room temperature. Copper samples were then annealed at 150 O C to 650 O C annealing temperatures and positron lifetimes were also measured for these samples and then analyzed using the LT9-2 software. The results obtained show that the average lifetime first decreases with increasing temperature (due to disappearance of some defects in the samples) and then increase due to appearance of some new defects for example creation of grain boundaries in the sample. Keyword : Positron Life time Spectroscopy, 22 Na Source, coincidence system, time resolution, vacancy, defect in samples,positronium ,annealingtemperature