6 LiF small neutron detectors with an optical fiber have been used to measure 6 Li(n,)T reaction rate distributions at thermal research reactors and accelerator facilities. In the present study, we developed an experimental method for the measurement of tritium production rate (TPR) of 6 Li using this small detector in deuterium-tritium (D-T) neutron fields. Reaction rate measurements with the detector were conducted in the D-T neutron fields at the Fusion Neutronics Source (FNS) facility. From the results, we determined that this detector can be used to measure the TPR distribution in soft neutron spectrum fields such as in a Be assembly. It is difficult to obtain 6 Li(n,)T reaction rate separately in hard neutron spectrum fields such as in a Li 2 O assembly, because many kinds of charged particle production reactions need to be taken into consideration. However, a time-dependent reaction rate measurement method combined with the 6 LiF detector and the ZnS detector is effective to separate the 6 Li(n,)T reaction from other reactions even in a hard spectrum field, and it can be applied to the measurement of the TPR distribution accurately.