Healthy seaweed salt is low sodium salt from seaweed that offers health benefits for hypertension patients. Indonesian seaweed has the potential to produce healthy seaweed salt. Research to date still focuses on green and brownseaweed but there is still no report for red seaweed. Actinotrichia fragilis isone of red seaweed species that has been discovered in Indonesia’s seawaterand has not yet been utilized. Thus, this study aimed to determine the chemicalcomposition and antioxidant activity of A. fragilis flour and the optimum ratiofor producing seaweed salt with a high yield, optimum %NaCl, Na/K ratio, andantioxidant activity. Seaweed salt production treatment was the ratio of seaweed flour and distilled water 1:3, 1:5, and 1:10 (w/v), extracted at 40°C for 10minutes. The mixture was filtered, then dried at 60°C for 30 hours. Data analysiswas performed by analysis of variance. The raw material for dried A. fragilisseaweed has a high ash and low-lipid content. Then the ethanol extract had atotal phenolic content value of 84.34 mg GAE/g and an antioxidant activityvalue of 98.22 mg/L. Furthermore, the antioxidant capacity of the ethanol extract was 60.15 nmol ascorbic acid/g and 552.21 n mol Fe2+/g. The best treatmentfor producing A. fragilis salt is 1:10 with yield of 12.76±0.13%, %NaCl47.22±1.38%, Na/K ratio 3.32±0.18, IC50 with DPPH and ABTS method 113 mg/Land 87.27 mg/L, total antioxidant capacity 38.21 n g/mL ascorbic acid/g, and304.32 n mol Fe2+/g. Furthermore, A. fragilis can be used for the production ofhealthy seaweed salt.