Transmission tower networks play an important role in the infrastructure system of many countries around the world. Many studies have been directed towards the evaluation of aerodynamic coefficients of the vertical tower body sections of transmission towers. Most of these studies obtain drag coefficients of tower sections from wind tunnel tests with yawed wind. However, strong winds like hurricane, downburst, tornado etc., which are the leading causes of transmission tower failures, often attack the towers with both yaw and tilt angles. Transmission towers constructed on the top or slope of mountains may also suffer the action of skew winds with both yaw and tilt angles. This paper addresses wind loads of transmission towers under winds with both yaw and tilt angles. By performing wind tunnel tests with multi-balance synchronous force measurement, the wind loads acting on a lattice tubular steel transmission tower under skew winds were measured, and the drag coefficients under 19 yaw angles and 13 tilt angles were obtained. Besides providing a more accurate modified formula for the skewed wind load factor, concepts of tilted and combined wind load factors are proposed with recommended formulas. By comparing the experimental and standard-calculated values of skewed wind load factor under a tilt angle of 0°, it is found that the standards underestimate the skewed wind load factor by at least about 10%, whereas the error of the proposed formula is less than 4% under the design key angles. In this study, the values of tilted wind factor under a yaw angle of 0° and combined wind load factor are recommended as 0.3 and 0.2, respectively. When the recommended values are used in calculation, the deviations between calculated drag coefficients and wind tunnel test results are less than 5%.