A noncircular, liquid-condensed domain is created in liquid-expanded surroundings of a methyl octadecanoate Langmuir monolayer upon fusion of two circular domains using optical tweezers. After fusion, the relaxation to a circular shape is observed using fluorescence microscopy. The relaxation rates of the Fourier components of the shape deformation are proportional to the order of the Fourier component and in the range of 1 s(-1). This shows that the relaxation is dominated by the surface shear viscosity eta (i) = 0.41 +/- 0.1 mu Ns/m of the liquid-condensed phase.