Chemical investigation of the cyanobacterium <i>Dolichospermum</i> sp. NIES-1697 afforded nostosin G (<b>1</b>), a linear tripeptide, spiroidesin B (<b>2</b>), and two known compounds, anabaenopeptins I (<b>3</b>) and J (<b>4</b>). Planar structures and absolute configurations for <b>1</b> and <b>2</b> were determined by 2D NMR, HRMS, Marfey's methodology, chiral-phase HPLC, and enzymatic degradation. Nostosin G (<b>1</b>) is a unique example of a linear peptide containing three subunits, 4-hydroxyphenyllactic acid (Hpla), homotyrosine (Hty), and argininal, with potent trypsin inhibitory properties. The biosynthetic gene clusters for nostosin G (<b>1</b>) and spiroidesin B (<b>2</b>) were investigated based on the genome sequence of <i>Dolichospermum</i> sp. NIES-1697.