Clinacanthus nutans or Belalai Gajah is one of the herbs that contain natural antioxidant. This natural antioxidant can be used commercially in food as well as pharmaceutical industries. This research explored antioxidant of C. nutans and it was extracted by using solid-liquid extraction. Antioxidant of C. nutans extract was determined by using 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay and Total Phenolic Content (TPC) were determined using Folic-Ciocalteau reagent. Screening of the suitable particle size to be used in the extraction of C. nutans shows that mixture and leaves of C. nutans with particle size <63 μm was the best to obtain the highest DPPH scavenging activity. However, only mixture of C. nutans sample was used for the thermal extraction kinetic due to the availability of the samples. Thermal extraction kinetic of DPPH was fitted to the exponential growth model and show a good fit with R^2 = 0.9921. When transformed, the data gave a linear Arrhenius plot, R^2=0.717 with an activation energy of 17.35 x 0.108 kJ/mol. Thermal extraction kinetic of TPC was fitted to the exponential growth model and show a good fit with R^2 = 0.9892. When transformed, the data gave a linear Arrhenius plot, R^2=0.897 with an activation energy of 5.3832 x 0.451 kJ/mol. The model is adequate to predict DPPH scavenging activity and TPC of the C. nutans extracts with no significant different of the prediction and validation conducted at temperature of 70 °C for 30 min.
