The aim of this thesis was to investigate different performance aspects of two reverse proxy cache servers which are called Varnish and Apache Traffic Server. It uses the tool Web Polygraph to generate various types of web traffic workloads.Both artificial and realistic workloads were designed and generated for each proxy in an identical test set up. In addition several system metrics(so-called Surrogate tests) were collected simultaneously to have the overview of overall system performance.For the experiments conducted in this research, the results indicated that Apache Traffic Server reached better cache hit rates and slightly better bandwidth throughput with the cost of higher system and net work resource usage. Varnish on the other hand managed to response higher request rates with better response time, especially for the cache hits. The findings in this thesis indicates that Varnish seems to be more promising reverse proxy.