We study de nonlinear optical properties of three ionic liquids of family [BMIM]. The ionic liquids are 1-buthyl-3-methylimidazolium tetrafluoroborate, 1-buthyl-3-methylimidazolium trifluoroacetate, and 1-buthyl-3-methylimidazolium Bis((trifluoromethyl)sulfonyl)imide. We calculate the static molecular polarizability (α) and hyperpolarizability (β,γ) using PM3 model and determinate experimentally the third-order nonlinear optical susceptibility χ(3), using z-scan technique. Interest in nonlinear optics has grown in recent years. High performance electro-optic switching elements for telecommunications and optical information processing are based on materials with high nonlinear optical (NLO) properties. This NLO are presents when a laser interacts with the materials, and can be studied at to levels: molecular o bulk.