Our previous studies demonstrated significant inhibition of Ehrlich ascites carcinoma (EAC) growth when using nanocomposites, namely nanoparticles (NPs) of rare-earth metal orthovanadates GdYEuVO4 and nanocomplexes (NCs) based on them with the addition of cholesterol. In the implementation of the antitumor effect of NCs, scavenging receptors present on transformed cells may be involved, which, among other functions, play a leading role in the absorption of cholesterol molecules. It is scavenging receptors on tumor cells that can capture NCs, due to which the latter penetrate the cell, turning on mechanisms that cause cell death. Our research aim was to investigate the mechanism of antitumor action of nanoparticles of rare-earth metal orthovanadates GdYEuVO4 or nanocomplexes based on them and cholesterol after incubation in vitro with Ehrlich ascites carcinoma cells. The research object was EAC cells, which were transplanted intraperitoneally into BALB/c mice. On day 7 of EAC development, the cells were isolated and in vitro treated with NPs or NCs for 3 h. Untreated cells were used as controls. After incubation of cells with nanocomposites, the number of CD44+ cells and ROS-positive cells, the one of cells in a state of apoptosis or necrosis, and the percentage of EAC cells positive for the Ki-67 marker were determined with a FACS Calibur flow cytometer (BD, USA). After treatment with NPs and NCs, the subpopulation composition of EAC changed due to a reduced number of CD44high and CD44+CD24– cells. When using NCs and NPs, the number of ROS-positive cells was observed in 3 and 2.4 times higher (respectively) among EAC cells compared to the control. NPs use led to cell death by both necrosis and apoptosis, while NCs mainly contributed to an increase in the percentage of necrotic cells. It was shown that NCs inhibited the proliferative activity of EAC cells to a greater extent than NPs, that was confirmed by a reduced number of Ki-67+ cells. According to the totality of the studied parameters, nanocomplexes were able to exhibit a more pronounced antitumor effect than nanoparticles. This phenomenology may be stipulated by the targeted capture of cholesterol by scavenger receptors, being a part of the nanocomplexes.