Water-induced formation of reverse micelles from polystyrene-b-poly(N-isopropylacrylamide) (PS(x)-PN(y), where x and y were the degrees of polymerization of PS and PN blocks, respectively) in 1,2-dichloroethane (DCE) was investigated mainly by light scattering. Four PS(x)-PN(y) samples with different degrees of polymerization x and y were prepared by the reversible addition fragmentation chain-transfer (RAFT) radical polymerization technique. While PS(x)- PN(y) was molecularly dispersed in DCE, the addition of water remarkably enhanced scattering light intensity from the DCE solutions of all the PS(x)-PN(y) samples, indicative of the formation of the reverse micelle having a water pool as the micellar core. Static light scattering (SLS) data for PS(x)-PN(y)/water/DCE ternary systems were analyzed using a model of spherical reverse micelle to estimate structural parameters, which were dependent on the hydrophilic-hydrophobic balance, i.e., y/x.