The suitable refinning degree of Japanese black charcoals has been studied by writers. As the experimental materials, we used the black oak charcoal and we cut them 8-9cm and tested by the ref inning meter, and divided 5 groups by refinning degree, 1-2, 3-4, 5-6, 7-8, 9. Each group was accepted a combustion test and studied the relationship between refinning degree and combustion state. We have found that the suitable refinning degree was 6-7, judging from heat efficiency and combustion time.