Urban trees are widespread trees and vegetation occurring within a populated area, they include all trees on public and private lands, eg, parks, sidewalks, public buildings, roads, etc. They play a vital role in the environment as well as human beings, eg, they improve air quality, reduce energy demand for heating & cooling, conserve biodiversity, etc. This book shows the effect of urban trees on Oxygen & Carbon dioxide concentration, Relative humidity, Air temperature and Wind speed: Case study Khartoum State - Sudan. Collected data were analyzed by SPSS & Excel. 28 Statistical models were built to show the relationship between the readings under trees as the dependent variable and that at the bare land as independent one.