The phytochemical studies revealed that jackfruit (Artocarpus heterophyllus Lam.) was rich in bioactive compounds including mainly carotenoids, flavonoids, volatile acids, tannins, and lectins, which are responsible for several biological activities. The purpose of the present study was to analyse biological activity of (1 ® 4)- b - galactans isolated jackfruit in the field of immunomodulatory, cytotoxic and anti-oxidative effects connected with human colon carcinoma cells viability and proliferation. The biological activity of galactans from Artocarpus heterophyllus revealed no toxic influences on viability of human colon tumor cells (HT29 and SW620) analyzed by Neutral Red (NR) uptake assay. After 24 h and 48 h of incubation cellular viability was no lower than 94%. Similarly, metabolic activity of cells (MTT test) at the highest compound concentration (250 m g/mL) applied was higher than 92% in comparison to control. At the same concentration, galactans had no significant influence on morphology of cells as visualized by May-Grünwald-Giemsa (MGG) staining. Nitric oxide production by tumor cells after their incubation with galactans showed changes in the radical level dependently on time of incubation and previous cells’ 2 h stimulation with endotoxin (LPS). Tested galactans stimulated significant amounts of IL-1β production by HT29 and SW620 cells. The compound at the concentration of 200 m g/mL stimulated almost 2-times higher (5.7 pg/mL) amounts of the cytokine as compared to the level released by HT29 cells. IL-6 level increased but IL-10 decreased in a galactans concentration dependent manner after incubation with HT29 cell culture. The effect was not detected in SW620. Tested galactans had strong concentration dependent reducing activity of DPPH and Fe3+ ions. The highest galactans concentration applied (250 m g/mL) reduced DPPH at the level corresponding to 16.2 m g/mL of Trolox, while in the case of FRAP method it was equivalent to 48.4 m g/mL of ascorbic acid.