Aggregation of fullerene C₆₀ with the solvent molecules in N-methylpyrrolidone solutions have been studied by the spectral and electrooptical methods. The time evolution of electronic absorption and photoluminescence spectra of solutions at the various initial concentrations of the solute has shown that the aggregation process is strongly concentration dependent. A comparison of spectral data with the electrooptical properties of solutions made it possible to conclude that at the concentration range <0.05×10^-2 g cm^-3, a process of complex formation between C₆₀ and N-methylpyrrolidone molecules takes place.