As some researchers pointed out, Ulisse Aldrovandi’s tavole acquarellate and the Atlas de Historia Natural (known as Códice Pomar, offered by Felipe II of Spain to the physician Jaume Honorat Pomar from Valencia), share a number of almost identical visual representations of animals and plants. A close analysis confirms that is the case for more than one hundred illustrations from the two collections. We present some working hypothesis in order to try to understand this coincidence and contribute to the comprehension of the mechanisms of circulation of knowledge between Italy and Spain in the second half of XVI century.