Lyophilised nagami kumquat (Fortunella margarita) powder was extracted with five different solvents. Dried extracts of EtOAc and MeOH–water (4:1, v/v) had the highest and lowest total phenolics, respectively, by Folin–Ciocalteu method. LC–MS analysis confirmed the presence of different levels of rutin, narirutin, poncirin, apigenin 8-C-rutinoside and 3′,5′,di-C-β-glucopyranosyl phloretin in all the extracts except n-hexane. EtOAc and MeOH extracts exhibited the highest and the lowest 1, 1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity, respectively. The order of antioxidant capacity was found to be MeOH–water (4:1, v/v)>EtOAc>MeOH>n-hexane>acetone by phosphomolybdenum complex and oxygen radical absorbance capacity (ORAC) values. Among five extracts, n-hexane extract exhibited the highest inhibition of human prostate cancer (LNCaP) cells (86.4%) after 96h at 100μg/mL, followed by EtOAc (82.8%), MeOH (76.7%) and MeOH–water (4:1, v/v) (68.2%). Fragmentation of DNA suggests the ability of extracts to induce apoptosis in LNCaP cells. The cleavage of caspase-3 was the highest in n-hexane and EtOAc extracts, whereas the ratio of Bax/Bcl2 was the highest in MeOH and MeOH–water (4:1, v/v) extracts. The results of the present study were also supported by fluorescent images of LNCaP cells treated with kumquat extracts. The maximum cell proliferation inhibition activity of n-hexane extract may be due to the presence of one or cumulative effect of β-carotene, β-cubebene and hexadecanoic acid. Remaining four extracts exhibited differential antioxidant activity and cytotoxicity which may be due to the presence of various levels of rutin, narirutin, poncirin, apigenin-8-C-rutinoside and 3′,4′-di-C-β-glucopyranosyl phloretin in each extract.