This invention relates to marine algae, and more particularly, to a method for producing improved seaweed strains by genetic engineering. The vector for transformation were constructed by inserting the high-plant or algae-derived promoters upstream of foreign reporter genes or such cassettes that functional genes are fused with antibiotics or herbicide-resistant genes. The genetic seaweed was generated by natural development process by recombinated plasmid DNA introduction to seaweed spore with Biolostics as transformation methods. Introduced traits of antibiotics or herbicide-resistance were used to select the transgenic seaweed individuals when foreign functional genes are transformed. Stable transformation could be obtained following this invention.