The first hyperpolarizabilities ('beta') of four azobenzene derivatives are measured via hyper-Rayleigh scattering (HRS) technique at 1064 nm. These compounds show weak absorbance at 532 nm and neglectable two-photon fluorescence (TPF). Their static first hyperpolarizabilities ('beta0') are estimated by the classical two-level model. The effects of varying the variety and number of the acceptors from chloro to nitro substituents are studied. It is concluded that the first hyperpolarizabilities will be enhanced with increasing polarity or number of the acceptors, attributed to improved transferability of their 'pi'-conjugated electron clouds.