Extravasation of antineoplastic agents is cited as a cause of ulceration, blistering, and induration. Delays in detecting extravasation can lead to severe skin damage, making detection as early as possible crucial. Clinical identification has previously been based on patients' accounts of pain and nurses' observations of erythema and swelling around the tip of the catheter. However, because pain and erythema may also occur as a result of drug-induced irritation of the vessel walls, cases are sometimes difficult to identify accurately. This research focused on the use of thermography as a method of identifying the presence of extravasation objectively. Extravasation was defined as swelling around the infusion site during administration or as subcutaneous hemorrhage, erythema, pigmentation, induration, blistering, or epidermal loss occurring at any time before the next visit. Of 257 patients who received chemotherapy through peripheral veins, extravasation was identified in 26. Thermography was performed every 15 to 30 minutes during the infusions. A low-temperature region with a gradual decrease in temperature from the infusion site margin was seen in the extravasation group. Sensitivity, specificity, positive predictive value, and negative predictive value using thermography were 85%, 95%, 65%, and 98%, respectively. This study showed that thermography offers an accurate method of identifying extravasation. Use of devices based on nursing science and engineering contributes to the development of new nursing technology.