Seaweed is increasingly being explored as an ingredient within functional foods due to the favourable nutritional characteristics that can be leveraged from the underutilised sea vegetable(1). Despite being a nutritionally dense and environmentally sustainable food source, seaweed is still commonly considered a novel food among many Westernised consumers(2), and this limits the potential consumer interest in novel food products containing seaweed. Fermentation presents an opportunity for seaweed to undergo changes to the sensory profile that may improve consumer appeal while simultaneously maintaining or further enhancing the nutritional composition. The development of a fermentation process for Australian sea lettuce, the green seaweed Ulva ohnoi, was conducted to explore the effects of fermentation on the biochemical, microbial and nutritional characteristics of the seaweed. The method of fermentation was repeated several times to optimise each stage of the fermentation process. U. ohnoi was harvested, rinsed under fresh water, drained, either processed immediately as fresh biomass or dehydrated, frozen, and then processed as dried biomass, then combined with filtered water, 5% (w/v) glucose, and inoculated with 0.05% (w/v) Lactiplantibacillus plantarum. Fermentation was conducted at 30 ˚C for 48 hours. Samples were then dehydrated and frozen for subsequent analysis. The process was repeated to obtain four replicate samples of fresh fermented U. ohnoi, dried fermented U. ohnoi, and dried non-fermented U. ohnoi as control. Samples were analysed for pH level, proximate composition, trace element content, heavy metal content, and microbiological content. A food-safe pH of ≤ 4.6 was typically achieved within the first 24 hours of fermentation and maintained throughout fermentation. Microbiological measurements were performed after 48 hours of fermentation and were all within the acceptable limits as stipulated by Food Standards Australia New Zealand. Iodine content across all samples ranged from 24-26 mg/kg which can contribute favourably towards the Recommended Dietary Intake of 150 µg/d. The effect of fermentation on the proximate composition, trace element and heavy metal composition will be presented in the context of the Australian Nutrient Reference Values and Food Standards Australia New Zealand Standards. The results indicate that fermentation processing was effective, as indicated by a food-safe pH level and microorganism and iodine content compliant with food-safe limits. This research consolidates a method of fermentation that is appropriate for both fresh and dried U. ohnoi and likely also applicable to other seaweed species. Fermentation may be a viable method to increase the seaweed appeal amongst Westernised consumers, which is now being evaluated via sensory evaluation. These findings can also be valuable to inform the fermentation of seaweed beyond food-related outputs such as nutraceuticals and animal feed.