Recently tendency could be noticed that the intelligence powers of not only national intelligence and security agencies, but that of regular police should be empowered, also with intent to gather evidence for subsequent criminal prosecution. This trend could be recognised also in Slovenia. It is connected to data mining, since the police intelligence activity includes the acquisition, assessment and analysis of personal and other data about criminal activity of natural and legal persons and criminal associations according to police legislation. Based on this, the process of decision-making and planning of police activity regarding crime prevention, detection and investigation should be made. In this framework, the Police can gather information from all public sources and with cooperation of persons, who voluntarily give the police operational information about criminal acts, perpetrators and other relevant activities. This increased police intelligence activity of course opens up also numerous legal issues and question. From the viewpoint of compatibility of with Criminal Procedure Act it is also of great significance, when this intelligence activity transforms into criminal procedure, in which stronger encroachments of privacy are allowed, but in which also the status of a suspect carries certain legal protection. And last, but not least; it is essential, whether the police is allowed to use its own - already existing - official records of personal data, or even the official records of personal data, kept by other state authorities, since the Slovenian personal data protection is relatively strict. This paper therefore explores data mining, conducted by the Police during its intelligence police activity in Slovenia, and its legal limits.