Scientists have explored the magnetic field in upper solar atmosphere by observing the polarization of ultraviolet light with the CLASP sounding rocket experiment during its 5-minute flight in space on Sept. 3, 2015. The data show that the structures of the solar chromosphere and transition region are more complicated than expected. It is proven that ultraviolet spectropolarimetry can be used in future investigations of the magnetic fields in upper solar chromosphere and transition region.