Background: Oxidative stress and impaired cholinergic neurotransmission are central features of Alzheimer’s disease. Plant-derived inhibitors of butyrylcholinesterase (BChE) may provide useful leads for neuroprotective research. Objective: To compare the influence of plant species and extraction-solvent polarity on the BChE inhibitory and DPPH radical-scavenging activities of cucurbitaceous seed extracts and Hydrocotyle asiatica. Methods: Seeds of Cucurbita maxima, Cucumis melo, Cucumis sativus, and Citrullus lanatus, together with whole-plant material of H. asiatica, were sequentially extracted with petroleum ether, chloroform, ethyl acetate, and methanol. BChE inhibition and DPPH scavenging were evaluated in triplicate at 0.2, 0.5, and 1.0 mg/mL, using galantamine and ascorbic acid as reference compounds. Results: The methanolic extract of C. lanatus was reported to inhibit BChE by 81.19% at 1.0 mg/mL (IC50 = 98 µg/mL). The ethyl acetate extract of C. maxima produced 81.77% inhibition, whereas the chloroform extract of H. asiatica reached 88.88% inhibition at 1.0 mg/mL. In the DPPH assay, the chloroform extract of C. sativus showed the strongest seed-derived activity (63.78% at 1.0 mg/mL; IC50 = 642 µg/mL), followed by the ethyl acetate extract of C. lanatus (IC50 = 708 µg/mL). Conclusion: Bioactivity depended strongly on both species and solvent. The most active fractions warrant bioassay-guided isolation, mechanistic enzyme-kinetic studies, and in vivo validation; the present findings should be interpreted as preliminary in vitro evidence rather than proof of therapeutic efficacy.