A 44-year-old Midvale man faces Midland Magistrates Court today on one charge of possessing child exploitation material.
The man was arrested after Perth Transit Authority officers saw him acting suspiciously on a train bound for Midland about 4pm on June 2.
Police searched his phone and allege they found several sexually explicit images of young girls.
A police spokeswoman said each image, photograph or movie of this type represented a child being abused.
Other electronic storage devices were also seized and further charges may be laid after analysis of the devices.
Police would like to speak to the man who reported the incident to the Perth Transit Authority officers and anyone else who saw any suspicious activity on this Midland-bound train.
Anyone with information can call Crime Stoppers on 1800 333 000.