Monitoring the temperature inside superconducting magnets is an effective way to detect failures and prevent damage to the magnet. It is possible to measure the multipoint temperatures with one optical fiber sensor thread. The sensor is suitable for measuring the temperature inside cryogenic equipment because of its low heat invasion and high voltage insulation in comparison with the resistance temperature sensors such as CERNOX, thermocouples, etc. However, there have been almost no cases where the optical fiber sensors have actually been used at cryogenic temperature. Investigations where therefore carried out into optical fiber temperature sensors that can be used at cryogenic temperature, to monitor the temperature inside superconducting magnets.