Cyanobacteria produce a wide variety of bioactive compounds, making them a highly promising group in the search for novel molecules with pharmacological and biotechnological properties. Among these, microginins attract attention for being peptides which inhibit angiotensin-converting enzyme, turning them into potential targets for hypertension and congestive heart failure treatment. This work describes a rapid and sensitive method for untarget screening of microginins in cyanobacteria extracts by LC-QqQ-MS/MS. These compounds are mostly characterized by containing 3-amino-2-hydroxy-decanoic acid at the N-terminus, which often could be chlorinated, dichlorinated or methylated. Based on the fragment ion arising from this decanoic acid derivative, a precursor ion scan (PIS) strategy has been proposed. This approach identified suspect microginins in cyanobacterial strains and environmental samples that were later confirmed by LC-QTOF-MS/MS. Eight new microginins structures were characterized based on the obtained fragmentation spectra from a total of 19 variants detected. This study highlights the applicability of PIS mode acquisition for untarget screening, detecting a wide variety of microginins with amino acids modifications, produced mainly by Microcystis aeruginosa strains. This method is a useful tool for the identification and environmental monitoring of molecules with conserved molecular substructures that possess similar fragmentation pattern