The influence of ambient condition on the β-carotene content of TNG66 sweet potatoes during storage was studied. TNG66 sweet potatoes are an original Taiwanese sweet potato cultivar. The annual yield of TNG66 sweet potatoes is 48.0 ton/ha. Because they contain significant amount of β-carotene (1.14 mg/g, on dry weight basis), TNG66 sweet potatoes have excellent bio-functionalities. On the current market, TNG66 sweet potatoes are generally stored under ambient condition. However, the ambient condition should not be used to store sweet potatoes. The warm temperature resulted in spouting and causing the degradation of active components. The degradation reaction was analyzed by a kinetic model. TNG66 sweet potatoes mainly contained all-trans β-carotene. When TNG66 sweet potatoes were stored under ambient condition, 58.8% β-carotene degraded after 21 days. In addition, 96.5% β-carotene degraded after 105 days. The kinetic model of β-carotene degradation was first order. The reaction rate constant was 0.034 (day^(-1)). The results of this study were useful for sweet potato manufacturers when storing and processing TNG66 sweet potatoes.