Many astrophysical fluids are strongly magnetized and in turbulent state. Since magnetic fields affect many physical processes, measuring their properties is of great importance. First, I will briefly talk about physics of Alfvenic MHD turbulence in strongly magnetized media, which will be the starting point of further discussions. Second, I will talk about the a technique to measure strength of magnetic field. Interstellar dust grains tend to be aligned with magnetic field and aligned grains emit polarized emission. Therefore, if we observe polarization by dust grains, we can derive information about magnetic field. In this talk, I focus on the Davis-Chandrasekhar-Fermi (DCF) method, which is a simple and power method to measure strength of magnetic field from polarization observations. I will also discuss how we can improve the method.