UV-curable LSR can be molded at relatively low temperature condition, which has advantages for an over-molding with inserts of temperature-sensitive materials. As the light sources for the radiation-cure process, halogen or mercury UV lamps have been used conventionally. However, the conventional lamps dissipate a lot of heat and their service life is relatively short. As substitution for the lamps, UV LED lamps provide a longer service life and a lower heat dissipation. In this research, UV LEDs were tested to analyze the rheological behavior of UV-curable LSR during curing process. UV-LEDs of various wave lengths and intensities were tested. The steady shear test was applied to find the starting time of cure and the SAOS was applied to find the ending time of cure. In addition, the hardness change along the curing time was compared with the rheological test result to make sure the reliability of the rheological test.