In the aqueous solutions the dephosphorylations of isopropyl phenyl-4-nitrophenyl phosphinate(IPNPIN) mediated by hydroxide$(OH^{ heta})$ and o-iodosobenzoate$(IB^{ heta})$ ions ate relatively slow, because of hydrophobicity of the substrate, and however it appears that $OH^{ heta}$ is inherently better nucleophile than $IB^{ heta}$, which is more soft ion. On the other hand, in cetyltrimetyiammonium bromide(CTABr) solutions which contain cationic micelles, the dephosphorylations of IPNPIN mediated by $OH^{ heta}$ or $IB^{ heta}$ ate very accelerated to 120 or 100,000 times as compared with those in the aqueous solutions. The values of pseudo first order rate constants reach a maximum with increasing. Such rate maxima are typical of micellar catalysed bimolecular reactions and the rise in rate constant followed by a gradual decrese is characteristic of reactions of hydrophobic substrates. In the cationic micellar solutions of CTABr, $IB^{ heta}$ accelerates the reactions much more than that $OH^{ heta}$ does. The reason seems that $IB^{ heta}$ which is more hydrophobic and soft ion than $OH^{ heta}$ is more easily moved into the Stern layer of the CTABr micelles than $OH^{ heta}$. In the anionic micellar solutions of sodium dodecyl sulfate(SDS), the dephosrhorylations of IPNPIN ate slower than those in aqeous solutions. It means that $OH^{ heta}$ or $IB^{ heta}$ cannot easily move and approach to the Stern layer of the micelle in which almost all the hydrophobic substrate are located and which has a negative circumstance.