Abstract: Determination of the angles between two planes is an important yet unsolved problem in descriptive geometry of N-dimensions. Available literatures all state that the problem can only be solved in a few particular cases, such as between two half-parallel planes, between two half-perpen -dicular planes etc1.Presents the unit circle method applicable in any conditions, thus suggesting a solution to problem unsolved for a long time in desriptive geometry of N-dimensions.