The Far Infrared (FIR) laser Stark spectrum ofSO2 was investigated using the 337 μm line of the HCN laser. Two distinct families, one originating at low field and the other at high field, were observed. The high field transition is identified as theJK−1,K+1=225,17←214,18, v2=1 transition. A significant fourth-order Stark shift was observed for this transition in the presence of a large second-order Stark shift. The zero-field frequency of the assigned transition was obtained by accounting for the fourth-order contribution.