Microalgae provides an excellent platform for foreign genes expression. Chloroplast and Nucleus based transformation of transgenes in algae is possible after construct designing (including different markers and promoters) and codon optimization. For better recombination, different and effective promoters and reporter genes can be selected. Chloroplast mediated transformation is much more effective than nuclear based transformation for transgene analysis owing to higher copy number of chloroplast in unit area. Microalgae based products are excellent target for production of wide variety of bio products such as vaccines, antibiotics and drugs against different diseases. These alternative approaches facilitate enhanced biodiesel production through fast growth of microalgae in heterotrophic environment. Also, low risks are attributed owing to their nonhuman consumption property. Biosafety and risk assessment analysis should be carried out before releasing of genetically modified microalgae in the environment considering research ethical code. Microalgae provide cheap, efficient and high yielding alternatives to plants. The review emphasizes microalgae based expression approach with key steps involved in detail.