The effect of solvent and extraction temperature on the initial antioxidant activity (AA) and total phenolic content (TPC) of Muitle (Justicia spicigera) extracts and their decay upon storage at different pH values was studied. Extraction with aqueous solvents, at either 25 or 60 °C, produced fresh extracts (pH 7.4) with higher initial TPC and AA. Extracts were adjusted to different pH's displayed different TPC and AA decay rates upon storage. TPC had first order decay kinetics, characterized by a relatively quick constant (k₁) at relatively short storage times followed by a relatively slow constant (k₂) at relatively large storage times. ABTS and DPPH assays estimated different AA in the extracts, attributed to compatibility differences between the bioactive species and the free radicals.