Spanish tax inspectors have been authorised to enter Google's offices in Madrid as part of an investigation.
A statement from Google said the company is co-operating with Spanish authorities and that it complied with Spain's fiscal legislation, as it does in all countries where it operates.
Leading newspaper El Pais and other media outlets said the searches at two Madrid offices are part of a tax evasion probe, but the Spanish tax agency has not commented.
The complex tax arrangements of Google and other technology firms have come under increasing scrutiny in many European countries in recent years.
French police raided Google's French headquarters in May as part of a similar investigation.