In this study, the aqueous extracts from selected medicinal plants were evaluated for their phytochemical composition, antitumor activity, and capacity to enhance the cytotoxic effects in combination with cisplatin on human cervical cancer cells (HeLa). In addition, their antioxidant properties were determined. The quantification of phenolic compounds and flavonoids on the extracts was performed by the Folin-Ciocalteu and aluminum chloride methods, respectively. The identification of phenolic compounds was determined by RP-HPLC-MS analysis. The evaluation of the cytotoxic effects of the extracts, cisplatin, and their combinations on HeLa cells was performed by MTT assay. The antioxidant activity was evaluated with the methods of DPPH, ABTS, and FRAP. According to the results, the extracts showed the presence of phenolic compounds and flavonoids; the identified metabolites mainly belonged to flavonols and hydroxycinnamic acids. Moreover, the extracts decreased the viability of HeLa cells, with the extracts from Artemisia ludoviciana and Parthenium hysterophorus with major cytotoxic activities. On the other hand, most of the combinations of the extracts with cisplatin enhanced the cytotoxic effects on HeLa cells, being the combination with the extract from Parthenium hysterophorus exhibiting the lowest percentage of cell viability. In addition, the extracts showed antioxidant potential, with the extracts from Mentha piperita, Origanum vulgare, and Tilia mexicana having the most significant antioxidant effects. The aqueous extracts demonstrated to be sources of phenolic compounds and flavonoids with cytotoxic activity on the HeLa cell line and the capacity to enhance the cytotoxic effects in combination with cisplatin. Moreover, the plant extracts showed antioxidant activity.