Excess salt intake could affect the immune system by shifting the immune cell balance towards a pro-inflammatory state. Since this shift of the immune balance is thought to be beneficial in anti-cancer immunity, we tested the impact of high salt diets on tumor growth in mice. Here we show that high salt significantly inhibited tumor growth in two independent murine tumor transplantation models. High salt fed tumor-bearing mice showed alterations in adaptive and innate immune cell subsets. Of note, depletion of specific innate immune cells significantly reverted the inhibitory effect on tumor growth. In line with this, high salt conditions almost completely altered the functional activity of these cells in vitro. Importantly, similar effects were observed in human cells isolated from cancer patients. Thus, high salt conditions seem to inhibit tumor growth by enabling more pronounced anti-tumor immunity through the functional modulation of this cell type. Our findings might have critical relevance for cancer immunotherapy.