Docosahexaenoic acid (DHA), an omega-3-fatty acid, modulates multiple cell functions. However, its role on the calcium transient of endothelial cells has not been investigated to date. Aim: we studied the effects of DHA on adenosine tri-phosphate (ATP)-induced human umbilical vein endothelial cell (HUVEC) calcium concentration. Methods: Cells were treated for 48-h with a low concentration (12.5 mM) of DHA. Then, cells were loaded with 5 mM fluorescent dye Fura-2AM and the ratio of free- calcium and bound-calcium (at 340/380 nm) was measured. Results: Cells treated with DHA exhibited a significantly reduced ATP (100 mM)-induced calcium increase (ACI) with a ratio of 2.54±0.03 in control versus 2.08±0.03 in DHA groups (P=0.000, N>=287, n>=8). When control cells were exposed to a calcium-saturated buffer and a calcium-free buffer, respectively, the ACI was decreased from 2.80±0.06 to 2.34±0.05, respectively (P=0.000). Interestingly, there was no significant difference between the DHA (2.41±0.06) and control groups (2.340.05) for the calcium-free condition (P>0.05, N>=120, n=4). In addition, the store-operated calcium (SOC) channel blocker, 2-aminoethoxy-diphenylborane (2- APB, 50 mM, 30 min) decreased calcium signal in cells untreated with DHA. Most importantly, no differences between DHA (2.08±0.05) and control (1.94±0.04) groups after 2-APB incubation (P=0.224, N>=100, n=4) were observed. Furthermore, calcium stores were depleted with 2 mM thapsigargin (TG), this caused a reduced increase of the cytosolic calcium concentration in DHA treated cells as compared to control cells (2.01±0.05 versus 1.85±0.04, P=0.000). A consecutive ATP stimulus applied after TG stimulation did not change the ACI between control and DHA groups (P>0.05, N>=60, n=2). Conclusions: 48-h treatment of HUVEC with a low concentration of DHA inhibited ATP-induced calcium transient. This is most likely due to an effect on the calcium influx via SOC channel.