Larvae of Paratrombium farnazae sp. nov. (Acari: Trombidiidae) were collected from soil samples (off their host) in forests in Roodbar and Rezvanshahr cities, and larval P. megalochirum (Berlese, 1910) were collected as ectoparasites of Tetramorium sp. (Hymenoptera: Formicidae) in Fuman city. All sites are in Guilan province, northern Iran. The new species is described and illustrated, and is the first recorded larva of Paratrombium with a bipectinate medial seta on coxae II and III in the world. Also, we report a species of the genus Paratrombiumin Iran for the first time and as an ectoparasite of the family Formicidae for the second time. A key to world larvae of Paratrombium is provided and the generic diagnosis is amended.