The Benchtop Micro-ESR, Active Spectrum, operates at 9.5 GHz with a sweep range of 500 Gauss and sub-micromolar sensitivity and equipped with a fast automated tuning system which provide easy and fast measurements. Also included is an automatic temperature controller for working at temperatures ranges from -80c to +100c. It runs under full Windows 7 computer system with Ethernet and multiple USB ports. The new bench top spectrometer is very useful for measurements of reactive oxygen or nitrogen species, spin labeling, spin trapping, kinetics etc.