We used ultraviolet, optical and infrared data of eleven HII regions in the Magellanic Clouds in order to determine their physical parameters and chemical abundances. The photoionization modeling of six HII regions in the LMC and five HII regions in the SMC, allowed us to derive the abundances of He, C, N, O, Ne, S and Ar, which were compared with those obtained in the literature for HII regions, PN, and stars. The abundances were obtained by adjusting models of the CLOUDY code to the observed line intensities. The observations obtained at the Observatório Pico dos Dias of [S II] λ6717/λ6731 line ratios for HII regions in the SMC allowed the determination of the electron density with a high precision. Furthermore, the IUE data on [C III] λ1909 lines were used to determine the abundance of carbon of six and five HII regions in the LMC and SMC, respectively.