The contemporary investigation was conducted to study the antimicrobial activity of Ulvales found in the coastal area of Karachi. The examined seaweeds( Ulva intestinalis, U. fasciata and U. lactuca. U. intestinalis) were collected from Sandspit and Kakkapir, whereas, U. fasciata and U. lactuca were gathered from Buleji. The selected species were examined to detect the antimicrobial activity against gram-positive Staphylococcus aureus, Staphylococcus epidermidis and gram-negative pathogen Shigella sp.  Accumulated bacteria- biofilms were found in the rocks of Buleji, Hawks Bay and Manora Island. It is remarkable to note that gram-positive and gram-negative bacteria are responsible for producing infectious diseases in humans. Seaweeds extracts were successively prepared in five solvents; namely, chloroform, ethanol, methanol, n-Hexane and distilled water. The present experiment was performed using the method of measuring the zone of inhibition followed by disc diffusion. Findings showed that U. fasciata and U. lactuca exhibited a scanty zone of inhibition against gram-negative and gram-positive strains. Although ethanol and methanol extract of U. intestinalis showed neither more nor less zone of inhibition against Shigella sp., yet aqueous solvent of seaweeds produced no activity against any bacteria.  Furthermore, recording the greatest zone of inhibition, the extract with ethanol showed the highest against the S. aureus. Notably, chloroform displayed a high limit of inhibition against S. epidermidis. It is worth mentioning that Sandspit collected U. intestinalis showed high bactericidal activity.