The aim of the study is to report Radopholus similis detected from Agathis dammara in Thailand as new host plant. Existing host of R. similis was known as coffee, pepper, sugarcane and banana etc. This nematode in this study was observed morphologic character using Carl Zeiss Axioimager M2 and Axiovision Rel. 4.8 program. The result shows that a and b of the female was distorted toward maximum value of original description of species, and b′, c and stylet length was distorted toward minimum value of original description of species. This nematode was morphologically distinguished from originally detected R. similis, but measured value was similar in range of original description of species. For more information, molecular assay was also confirmed the R. similis with 98% homology with the sequence of the internal transcribed spacer region (ITS) of ribosomal DNA. We provided PCR-amplified ITS nucleotide sequence.