Paraffin wax deposition is the most frequent flow assurance problem in oil production fields. It disrupts stable oil production, and a considerable amount of time and money are spent ameliorating on-site problems. To prevent and mitigate paraffin wax deposition, it is necessary to proactively identify the conditions under which paraffin wax is deposited. Furthermore, monitoring and detection techniques are required to determine the efficacy of the technical measures applied. This study proposes a method based on acoustic velocities obtained by ultrasonic monitoring and detection to estimate the following three temperature elements: (1) wax appearance temperature of oil containing paraffin wax, (2) temperature at which the growth of paraffin wax deposits is activated, and (3) temperature at which the paraffin wax deposits begin to age. An experimental system comprising an ultrasonic transducer and a temperature sensor were set up, and the temperature gradient of the analyzed fluid sample was controlled by continuously circulating an isothermal fluid. Based on real-time monitoring, data measurements were made, and variations in the acoustic velocity of fluid samples were measured. A paraffin wax deposition experiment was conducted using synthetic waxy oil samples with paraffin solid contents of 5 wt.% and 15 wt.%, respectively. Q-factors were calculated based on the spectral ratio method, and wavelet characteristics were analyzed according to temperature changes, to estimate wax appearance temperature. Results show that the method proposed in this study estimates wax appearance temperature in a similar measurement range as conventional methods and enables the life cycle of paraffin wax deposition to be determined through monitoring and detection.