The "MARS-3" Matrix Radiometric System for RATAN-600 Radio Telescope: Trial Observations D.V. Kratov Special Astrophysical Observatory of RAS The MARS (MAtrix Radiometric System) project is reported. The instrument is intended to be used as a radiometric support to the "Cosmological Gene" project. "Cosmological Gene" program is a new generation of the Ground Based experiment intended to the mapping of Cosmic Microwave Background Anisotropy (CMBA) at RATAN-600 radio telescope. Project sequential phases "MARS-1" - > "MARS-2" -> "MARS-3". - "MARS-1" (year 2001) - one radiometric module, that was developed and investigated in the "Total power", "Noise added radiometer" (NAR) and "Beam Switching" (BS) modes. As a result, BS mode was adopted for the phase 2. - "MARS-2" (year 2003) - more than 3 years round-the-clock operated 3-channel system (BS mode) with basic parameters: central frequency 30 GHz, bandwidth 4 GHz, Tsys = 220 K (sensitivity 6 mK(s1/2) for each channel). - "MARS-3"( year 2006) - 16-channel system (BS) with 5 GHz bandwidth, calculated Tsys = 200 - 210K, 5 mK(s1/2). It permits to accelerate the signal data storage up to the level required. "MARS-3" was installed in the focal line of the RATAN-600 radio telescope in April 2007. Test observations were carried out. The test observations showed effectiveness of the new matrix radiometric system.