Here, we use single molecule force spectroscopy performed with optical tweezers in order to investigate the interaction between Caffeine and the DNA molecule for various different concentrations of the alkaloid and under two distinct ionic strengths of the surrounding buffer. We were able to determine the mechanical changes induced on the double-helix structure due to Caffeine binding, the binding mode and the binding parameters of the interaction. The results obtained show that Caffeine binds to DNA by outside the double-helix with a higher affinity at lower ionic strengths. On the other hand, a considerable cooperativity was found only for sufficient high ionic strengths, suggesting that Caffeine may binding forming dimers and/or trimers along the double-helix under this condition. Finally, it was also shown that Caffeine stabilizes the DNA double-helix upon binding, preventing force-induced DNA melting.