Summary The aim of the study was to determine the effect of feeding a low and high level of microalgae (MA, high in C22:6n‐3) on the fatty acid (FA) composition and sensory attributes of beef. Thirty Charolais cross Limousin/Friesian heifers were fed one of the three diets (n = 10 per treatment): Control (no MA), low MA (LMA; inclusion rate of 15 g kg−1) or high MA (HMA; inclusion rate of 30 g kg−1) for 95 days before slaughter. Heifers fed HMA had a higher (P < 0.05) content of C20:5n‐3: eicosapentaenoic acid (EPA) and C22:6n‐3: docosahexaenoic acid (DHA) in the longissimus thoracis muscle than those receiving the Control (mean values for EPA of 0.5, 0.92, 1.20 and DHA of 0.31, 0.89 and 1.05 % of total FA for Control, LMA and HMA, respectively), and a lower n‐3 to n‐6 ratio (2.9, 1.9 and 1.6 in Control, LMA and HMA, respectively; P < 0.001). Steaks from animals fed either of the MA diets had a marginally higher (P < 0.05) ‘seaweedy flavour’ that was positively correlated with muscle C22:6n‐3 concentration. Steaks from animals fed HMA were rated as being higher (P < 0.05) in tenderness and had a lower (P < 0.05) shear force than those from Control fed animals. It is concluded that feeding microalgae at high levels can beneficially improve the health attributes of beef with only a few effects on sensory quality.