Calcination properties and related structural changes of ulexite (NaCaB(5)O(9)8H(2)O) and colemanite (Ca2B6O11.5H(2)O) have been investigated and possibilities of separation of ulexite from colemanite have been examined by utilizing different structural changes during calcination. TGA, thermal analyses of both ulexite and colemanite were determined The maximum dehydration peak of ulexite was obtained at around 190 degrees C. The structural changes were investigated by XRD and mineralogical examinations. It was observed that ulexite lost its crystal water gradually forming more porous and friable structure up to around 300 degrees C, above that it gained hardness and compacted during calcination. On the other hand colemanite lost its crystal water suddenly and was decrepitated at 390 degrees C. As a result of calcination tests, two alternating methods were proposed for the separation of ulexite from colemanite by adjusting the calcination temperature. In the first method, a ulexite and colemanite mixture was calcined at 450 degrees C for 30 minutes, during which ulexite gained hardness while colemanite was decrepitated. The calcined mixture was screened, producing ulexite concentrate as oversize with 96.63 % B2O3 recovery. In the second method, ulexite and colemanite mixture was calcined at 240 degrees C for 60 minutes, during which ulexite became friable while colemanite kept its original crystal structure so that it was separated from colemanite by semi-autogenous grinding, and then screening. The ulexite concentrate was obtained as undersize product with 98.43 % B2O3 recovery.