Geological su㏄essions of the Timor Island situated in the eastern part of the Lesser Sunda Islands are stratigraphically composed of the sedimentary formations ranging in age from Lower Permian to Recent. In these formations，the Baucau Limestone（Pleistocene）and the uplifted coral reef（Holocene）consist largely of porous，cavernous，greyish−white coral reef limestone. These limestones are well developed along the north coast in easten Timor，and characterized by karst topography.
A geochemical method in the field has been prelimiarily tested for the detection of phosphate，on the possibility of guano phosphorite in these coral reef limestones. The method is an approach of the yellow color reaction which has been used for the qualitative determination of phosphorus by the nitric acid and ammonium molybdate solutions. In thls paper，the application and usefulness of a geochemical field method for guano phosphorite exploration in eastern Timor are briefly described.