Objectives : The purpose of this study is to evaluate the quality of four different kinds of agarwood and analysis chemical constituents by GC-MS. Methods : Four source plants were two of Vietnamese agarwood, Indonesian agarwood and Myanmar agarwood. These plant materials were named sample No. 1-4. The chemical constituents of each agarwood were analysed by GC-MS. Results : GC-MS analysis showed that ${eta}$-selinene was found in all the samples. The Vietnamese agarwood, Sample 1, and 4 has contained 6.861% and 7.497% of ${eta}$-selinene and reached the highest level at the retention times 46.245 and 46.274 (min). Sample 2, the Myanmar agarwood has contained 1.608%, the lowest level of ${eta}$-selinene, and it also has contained about 20% of ${alpha}-,{eta}-,{gamma}$-eudesmol and 4.076% of valerianol. Sample 3, the Indonesian agarwood has contained 9.59% of ${eta}$-selinene, 9.493% of ${eta}$-selinene and shown its highest level (more than 19%) at the retention time 43.998 (min). Conclusion : It suggested that ${eta}$-selinene could be a standard marker to evaluate agarwood by GC-MS analysis.