Urban temperatures have become more important because the frequency and intensity of heatwaves will increase with the worsening urban heat island effects due to climate change. Recently, urban sensors are emerging as a new means of heat island analysis, and urban sensor data including temperatures were opened to the public in Seoul in 2020. However, there are insufficient cases of analysis and the differences from national weather observation are unknown. Accordingly, this study introduces the S⋅DoT (Smart Seoul Data of Things), an urban sensor in Seoul, and compared S⋅DoT temperatures with national weather observation (such as ASOS and AWS) temperature in order to facilitate heat island analysis using urban sensors. The result shows the S⋅DoT temperature is about 1-1.15 ℃ higher than ASOS⋅AWS during May to August 2020, which is due to differences in the height and installation environment, not in the performance of the equipment. S⋅DoT is installed in the urban environments at the height of approximately 3 m and measures the actual living temperature, whereas ASOS measures temperature in the controlled environment and AWS measures temperature from the higher position due to being installed on the top of a building. Therefore, we suggest that when using S⋅DoT together with rural AWS temperature to analyze the intensity of heat islands, calibration should be considered taking into account the difference between the two observations, and a better method is to calculate the heat island intensity only using S⋅DoT temperature in urbanized and non-urbanized areas without using rural temperature.