The optimum of culture time and concentration of alginate for antimicrobial activity of both potential strain L18 and L8 were carried out for 12h, 24h, 36h, 48h, 60h, 72h, 84h, 96h, 108h and 120h by agar well diffusion method. The cultured broth of two best parameters in the previous experiment was designed as bio-products for application on preservation of sea grapes after harvesting. The effectiveness of those bio- products was expressed in the number of pathogenic bacteria counted. The physiological state of sea grapes was reliably evaluated with a diving pulse-amplitude-modulation fluorometer quantifying the chlorophyll fluorescence parameter of maximum quantum yield of photosystem II (PSII, Fv/Fm). Results showed strain L8 was strongly inhibited against Pseudomonas sp. A1 and Klebsiella variicola S1 after 36h cultivation whereas the strain L18 was most inhibition Pseudomonas sp. A1, Enterobacter sp. T1, Citrobacter freundii A2 after 60h cultivation. The concentration of alginate which was the most effective for antimicrobial activity of L8 was 0.3% and L18 was 0.2%. The bio-products added treatments showed a lower number of pathogenic bacteria from 1000 to 10000 times than those in the control samples. Bio-products treatments had not shown significant differences in total phenolic content and chlorophyll-a. In addition, the data from PSII measurement showed that two treatments L8 plus 0.3% alginate and L18 plus 0.2% alginate yielded much better productivity of PSII than other two control samples. The shelf life of edible seaweed could be increased up to 10 days at room temperature, when it was sprayed with bio-products.