The first lady will make an official visit to King Juan Carlos and Queen Sophia of Spain per their invitation, but all activities on the trip are closed to the press.
The trip coincides with President Obama's birthday, which is Aug. 4. The day after, Obama will be in Michigan and his hometown of Chicago visiting auto plants.
Last June, the first lady privately vacationed with both of her daughters and mother in France and England. They visited French President Nicolas Sarkozy and his wife Carla and later met with Sarah Brown, the wife of then-British Prime Minister Gordon Brown.
Michelle Obama also took Sasha and Malia to the "Harry Potter" movie set for the former's birthday.