We performed the Shubnikov-de Haas (SdH) experiments of the low carrier heavy fermion compound URu2Si2 at high fields up to 34T and at low temperatures down to 30mK. All main SdH branches named alpha, beta and gamma were observed for all the measured
field-directions (H // [001] -> [100], [100] -> [110] and [001] -> [110]), indicating that these are attributed to the closed Fermi surfaces with nearly spherical shapes. Anomalous split of branch alpha was detected for the field along the basal plane, and the split immediately disappears by tilting the field to [001] direction, implying a fingerprint of the hidden order state. High field experiments reveal the complicated field-dependence of the SdH frequencies and the cyclotron masses due to the Zeeman spin-splitting associated with the Fermi surface reconstruction in the hidden order state with small carrier numbers. A new SdH branch named omega with large cyclotron mass of 25m0 was detected at high fields above 23T close to the hidden order instabilities.
