We tried to detect traces of past infection of the pine wood nematode, Bursaphelenchus xylophilus, in dead Pinus armandii var. amamiana trees using a commercial kit for detecting B. xylophilus. Wood samples were taken from 24 dead trees in Tanega-shima Island, that had died 0 to 9 years before the sampling time. Among the 8 trees in which B. xylophilus had been detected by the Baermann funnel method, only 2 trees which had died less than a year before testing were positive in the kit assay. On the other hand, 6 samples taken from trees that had died 4 to 9 years before testing proved to be negative for nematode infection. For the trees in which B. xylophilus had not been detected by the Baermann funnel method, only one newly dead tree proved to be positive using the kit. With these evidences, we can conclude that it is very important to collect wood samples from newly killed trees or dead trees to be preserved under proper conditions to prevent any significant deterioration in order to increase the reliability of pine wilt disease diagnosis, even when using a high-accuracy detection kit.