The effects of temperature, pH and the presence of: ascorbic acid on the thermal stability of folic acid were studied in both citrate – phosphate buffer (pH 3 – 5) and food system. Steady – state heating, in small tubes at three different temperatures (100, 110, 120℃) for various times were used to determine order of reaction, rate constant and temperature dependence of the rate of folic acid degradation. The degradation of folic acid in both systems were best described by a first order reaction. The kinetic reaction rate constant.(k) in citrate – phosphate buffer at pH 4.00, 120 ℃ was 2.192 x 10 ⁻⁵ S⁻¹ and the activation energy (E Subscript a) was 69.9 kJ mole⁻ ¹ As the ph decreased from 5.01 to 3.01 the kinetic reaction rate constant at 120℃ increased from 0.371 x 10 ⁻⁵ to 3.619 x 10 ⁻⁵ S⁻¹ But the stability of folic acid was apparently increased in the presence of ascorbic acid, the kinetic reaction rate constant at pH 4.02, 120℃ was 0.889 x 10 ⁻⁵ S⁻¹ The kinetic reaction rate constant in apple juice at 120℃ Was 2.558 x 10⁻⁵ S⁻¹ and the activation energy was 99.9 kJ mole⁻ ¹