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Three novel monomeric naphtho-&#947;-pyrones, peninaphones A&#8722;C (compounds <b>1</b>&#8722;<b>3</b>), along with two known bis-naphtho-&#947;-pyrones (compounds <b>4</b> and <b>5</b>) were isolated from mangrove rhizosphere soil-derived fungus <i>Penicillium</i> sp. HK1-22. The absolute configurations of compounds <b>1</b> and <b>2</b> were determined by electronic circular dichroism (ECD) spectra, and the structure of compound <b>3</b> was confirmed by single-crystal X-ray diffraction analysis. Compounds <b>4</b> and <b>5</b> are a pair of hindered rotation isomers. A hypothetical biosynthetic pathway for the isolated monomeric and dimeric naphtho-&#947;-pyrones is also discussed in this study. Compounds <b>1</b>&#8722;<b>3</b> showed antibacterial activity against <i>Staphylococcus aureus</i> (ATCC 43300, 33591, 29213, and 25923) with minimum inhibitory concentration (MIC) values in the range of 12.5&#8722;50 &#956;g/mL. Compound <b>3</b> exhibited significant activity against the rice sheath blight pathogen <i>Rhizoctonia solani</i>.