<p>This research aimed to assess the effects of ampicillin (AMP), chloramphenicol (CAM), hygromycin B (HygB), paromomycin (PR), and penicillin (PCN) on <i>Haematococcus lacustris</i>. The EC₅₀ and EC₁₀ values were determined for these five antibiotics. Based on their EC₅₀ values, HygB and CAM were both found to be non-toxic to <i>H. lacustris</i>. The effects of supplementing <i>H. lacustris</i> cultures with the EC₁₀ values of each antibiotic were additionally noted. The results revealed that the application of AMP and CAM enhanced the growth of <i>H. lacustris</i>. Among all, the <i>H. lacustris</i> culture grown with CAM (75.85&#xa0;mg/L) resulted in the highest cell number and biomass on day 14. On day 9, the levels of chl <i>a</i> and chl <i>b</i> in each antibiotic-treated culture were comparable to the control. On day 14, the astaxanthin concentration in the PR-treated culture was similar to the control, but the astaxanthin levels in the other antibiotic-treated cultures were lower. On day 14, compared to the control, the total protein level was lower in the remaining antibiotic-treated cultures, similar in the PCN-treated culture, and greater in the PR-treated culture. Except for cultures treated with AMP and CAM, the remaining antibiotic-treated cultures had higher total carbohydrate levels on day 14 than the control. Furthermore, on day 14, the biomass and cell count of the cultures treated with AMP and CAM were significantly higher than the control, while cultures treated with PCN, HygB, and PR were similar to the control.</p>