Recently a memristor (Chua, L. O. IEEE Trans. Circuit Theory 1971, 18, 507), the fourth fundamental passive circuit element, has been demonstrated as thin film device operations (Strukov, D. B.; Snider, G. S.; Stewart, D. R.; Williams, R. S. Nature (London) 2008, 453, 80; Yang, J. J.; Pickett. M. D.; Li, X.; Ohlberg, D. A. A.; Stewart, D. R.; Williams, R. S. Nat. Nanotechnol. 2008, 3, 429). A new addition to the memristor family can be nanoparticle assemblies consisting of an infinite number of monodispersed, crystalline magnetite (Fe3O4) particles. Assembly of nanoparticles that have sizes below 10 nm, exhibits at room temperature a voltage−current hysteresis with an abrupt and large bipolar resistance switching (ROFF/RON≈ 20). Interestingly, observed behavior could be interpreted by adopting an extended memristor model that combines both a time-dependent resistance and a time-dependent capacitance. We also observed that such behavior is not restricted to magnetites; it is a general property of nanoparticle assemblies as it was consistently observed in different types of spinel structured nanoparticles with different sizes and compositions. Further investigation into this new nanoassembly system will be of importance to the realization of the next generation nanodevices with potential advantages of simpler and inexpensive device fabrications.