In this investigation, mechanism of the thermal processes and effect of the mineralogical and structural modifications on the grindability of ulexite were investigated. The mechanism of the thermal reactions were examined by thermo-analytical methods including TGA and DTA. The mineralogical and structural modifications were investigated by XRD and SEM techniques, respectively. The results indicated that ulexite thermally decomposes within 60-500 was first transformed into NaCaB₅O₆(OH)₆ x 3H₂O and then NaCaB₅O₆(OH)₆ x H₂O and finally became as completely X-ray amorphous phase accompanied with the thermal processes in the sequence of two-stage dehydration and two-stage dehydroxylation reactions resulting in two endothermic DTA peaks at 151°C and 180°C further treatment caused two-stage recrystallization process resulting in an exothermic DTA peak at 636°C and an endothermic peak at 855°C. The changes in the grindability of ulexite were determined in terms of work index by the Hardgrove Grindability Test. The results showed that work index of ulexite was found as 7.11kWh/shton and decreased to 3.5 kWh/shton level within 200-280°C for 60 minutes. Further heating lead to 8.49 kWh/shtonat 640°C for 60 minutes.