To study the effect of propolis in crude form (CPP), prepared without any chemical refinement (CPP) on Dicentrarchus labrax under low-temperature stress, sea bass juveniles were randomly divided into three groups: a control group fed with basal diet and two treatment groups fed with basal diet supplemented with 1.25 and 2.5 g kg−1 of propolis. At the end of a 10-week feeding trial, sea bass were exposed to low-temperature stress at 12 °C for 24 h. The growth performance, RNA/DNA ratio and changes in serum biochemical parameters were investigated. Dietary intake of propolis stimulated the specific growth rate (SGR), feed conversion efficiency (FCE), RNA/DNA ratio and alkaline phosphatase (ALP) enzyme activity, while decreasing plasma triglycerides and aspartate aminotransferase (AST) activity. Supplement of 2.5 g kg−1 CPP in diet significantly increased the mean SGR and FCE up to 9% and 13.4%, respectively, in comparison with the control group. Low-temperature stress elevated serum triglycerides, glucose and cortisol levels in all groups; however, glucose and cortisol reached significantly lower end values in group receiving highest amount of propolis in diet. This study suggests that ingestion of basal diet supplemented with 2.5 g kg−1 of propolis could prevent adverse effects of low-temperature stress and promote the growth of sea bass.