Tritium benchmark experiments with D-T neutron are a key issue to verify the tritium production rate (TPR) of the fusion blanket. The most useful method to measure the TPR in the neutron benchmark experiments is the liquid scintillation counting with Li2CO3 pellet. Ten years ago, the method of Li2CO3 pellet has been sufficiently verified the accuracy by means of D-T fast neutron irradiation and it was concluded within 10%. However, on the recent breeding blanket design, tritium is dominantly produced with the thermal neutron made with the scattering of D-T neutron and also the accuracy of the tritium production rate is requested below 10%. Therefore, previous verification is not sufficient for the recent blanket design and it is necessary to carry out the activity of the verification again. The JAERI, ENEA and TUD began to carry out the tritium benchmark experiment to verify the tritium production rate for the recent fusion blanket.