[en] In the present work, radon concentrations in six caves of PETAR - Parque Estadual Turistico do Alto Ribeira (High Ribeira River Touristic State Park) were carried out with Makrofol E solid state nuclear track detectors (SSNTD) and used to assess the annual effective dose received by regional tour guides. The park has four visitation centers: Santana, Ouro Grosso, Caboclos e Casa de Pedra and receives nearly 40,000 people annually. The caves evaluated were Couto, Agua Suja, Laje Branca, Morro Preto and Santana, from Santana center and Alambari de Baixo from Ouro Grosso center, for being the most frequently visited caves. The exposure period of the SSNTD was, at least, three months, over a period of 26 months, from October 2003 to November 2005.The ²²²Rn concentrations lay in a range from 153 Bq.m^-3 to 6607 Bq.m^-3 and we observed that, in general, for chilly weather, the radon levels decrease. The annual effective dose, considering the most realistic scenario, with geometric mean concentrations, an equilibrium factor of 0.5 and annual exposure time for each cave, varied from 0.2 mSv.a^-1 for the Couto cave, strongly ventilated, to 4.0 mSv.a^-1 for the Santana cave, the most frequently visited and no external communication. For the worst scenario, with arithmetic mean concentrations, equilibrium factor 1 and annual exposure time for all caves, the annual effective dose was 16.1 mSv.a^-1. All assessed effective doses received by the tour guides are bellow 20 mSv.a^-1 suggested as an annual effective dose limit for occupational exposure by the International Commission of Radiological Protection (ICRP 60, 1990). (author)