Magnetoresistive effect has drawn a great deal attention in spintronics and microelectronic applications.^[1] Combining the advantages of low weight, low spin-orbit coupling and high thermal conductivity, graphene opens a suitable window for applications in magnetoresistance (MR) devices.^[2] It was reported that MR effect of graphene was derived from the edge states, which was regarded as main sources of the intervalley scattering, thus causing restoration of the weak localization (WL) localized.^[3] Moreover, previous studies indicated that introducing more edge states of graphene can improve the MR effect.^[4] Interest in nanoscale materials with large MR has been renewed due to the synergistic effect of quantum confinement and rich heterogeneous interfaces, the transport properties of electrons and magnetic properties will be significantly modulated.^[5] In particular, nanosized graphene was expected to be desirable candidates for achieving large MR. Herein, we constructed a vertically standing graphene nanocrystallines (GNs) embedded amorphous carbon film structure (VGC-film), and size dependent MR effect was observed from film with varied sized GNs ranging from 3.7 nm to 10.5 nm. Maximum MR value of ~8% was achieved at 2 K from VGC-film with 3.7 nm GNs, the MR value decreased with increasing size of GNs from 3.7 to 10.5 nm, this can be attributed to enhancement of wave function shrinkage effect. This work provides promising opportunities for constructing highly efficient MR devices using graphene nanocrystallines materials, like magnetic sensors, magnetic random-access memories and magnetic logic devices.

graphene,magnetoresistance,PVD thin film sensor