The French-Brazilian Micro-Satellite is a scientific satellite designed by France and Brazil. The satellite will be launched by the rocket ARIANE 5. The layout of the satellite was conceived to satisfy certain structural constraints such as: structural mass below 10.50 kg and first lateral frequency greater than 50 Hz. The initial design of the satellite has structural mass of 9.89 kg and first lateral frequency of 18.57 Hz. This frequency is far away from the minimum required. Therefore, changes had to be made in order to increase the first lateral frequency without violating the constraint of a maximum structural mass of 10.50 kg. The sensitivity analysis showed that the frequency was much more sensit ive to changes on the lower panel of the satellite. It was proposed a change with the purpose of stiffening the lower panel. Five reinforced design projects were analyzed. Two design projects were chosen which presented the best results. One project has a first lateral frequency of 30.88 Hz and the other one a frequency of 32.32 Hz. The two projects violated the structural mass constraint, with 10.70 kg and 11.24 kg, respectively. The optimization increased the frequency and reduced the structural mass at the same time. The largest frequency obtained was the one of the third project whose frequency was 33.16 Hz. The requirement related to the minimum frequency will have to be modified because it is very difficult to be satisfied by a structure with 10.50 kg of mass.