Up-conversion single photon detector technology has become efficient for photons in the near infrared range. However, its dark count rate is a major concern for some applications in quantum optics. We have theoretically and experimentally studied the causes of dark counts, and developed an up-conversion detector with an ultra low dark count rate. A reduced dark count rate of only 320 counts per second is achieved at the maximum overall detection efficiency of 18% and a dark count rate of less than 100 counts per second is achieved at a detection efficiency of 10%. The ultra low dark count rate enables this type of up-conversion detector to be utilized in a variety of applications where weak signals in the near IR region are only at a level of few thousand photons per second.© (2010) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.