Using simulation tools, this study investigates the effect of green walls (GWs) on the urban heat island (UHI) phenomenon within different street sizes. It can be planted without taking up more area and could enhance the microclimate environment, which is why it has a wide range of use potential in urban areas. Because Mina City has a threat of UHI, it was chosen for this study. The temperature within various street sizes in the research region was evaluated using only software called ENVI-met that simulates climate, and three common scenarios were chosen. In the first experiment, green walls extending over an area of 50 m in the south facades of the street building, including a 3m Street width, are simulated to show the effect of GWs on UHI. In the second experiment, the Street width changed to 6 m, and the GWs are placed in the same condition. The last experiment is the same with a 9m street width. Temperature decreases from each green wall were contrasted with the street canyon situation as it was at the time of evaluation 1's highest heat. In comparison to evaluation 1, the temperature decreases achieved by evaluation alternatives 2, 3, 4, and 5 were 2.17 °C, 1.97 °C, 1.78 °C, and 0.90 °C, accordingly. Conclusion: A well-planned urban green wall can significantly improve UHI in tropical Lebanon.