In this work, the effect of several carbon fillers, exfoliated graphite (EG), functionalized graphene sheets (FGS), multi-walled carbon nanotubes (MWCNTs), and oxidized multi-walled carbon nanotubes (f-MWCNTs), were compared on the curing process and physical properties of a cationically photocurable epoxy resin. The extent of the photopolymerization was monitored by Real-Time FTIR spectroscopy. It was found that all the nanofillers delayed the curing reaction probably due to a shielding effect as well as to an increase of the resin viscosity. All the systems showed an electrical percolation threshold, but with MWCNTs was attained at a lower concentration (<0.1 wt.%). In addition, FGS showed the best response in terms of the dynamic mechanical and microindentation performances. An increase of more than 20 °C in the glass transition temperature was observed with the addition of 1 wt.% of FGS.