Swelling behavior and deformations of main chain liquid crystal elastomers (MCLCEs) have been reported. The swelling agent used here is a low molecular weight liquid crystal (LMWLC), 4-n-pentyl-4-cyanobiphenyl (5CB). Monodomain MCLCE swells anisotropically with the swelling degree q(mono) = 11.9 and polydomain MCLCE swell isotropically in 3D with q(poly) = 12.1. These values are much larger than observed in swelling side-chain LCEs (SCLCEs). In the stress-strain measurement, the plateau area is found among two steep areas. The electromechanical effects of monodomain MCLCE is also observed, and the results show that the maximum contraction in parallel to(n) over cap n is about 7%. The threshold for the onset of the electromechanical effect is about 10 V, which is larger than observed in SCLCEs.