Olszewka may refer to the following places:

• Olszewka, Nakło County in Kuyavian-Pomeranian Voivodeship (north-central Poland)
• Olszewka, Ciechanów County in Masovian Voivodeship (east-central Poland)
• Olszewka, Ostrołęka County in Masovian Voivodeship (east-central Poland)
• Olszewka, Przasnysz County in Masovian Voivodeship (east-central Poland)

• Slender snouted crocodile
• Slender-spined porcupine fish
• Slender springtail
• Slender squirrel
• Slender stargazer
• Slender stylewort
• Slender suckerfish
• Slender sunfish
• Slender-tailed Cisticola
• Slender-tailed Deer Mouse
• Slender-tailed dunnart
• Slender-tailed Meerkat
• Slender-tailed nightjar
• Slender-tailed squirrel
• Slender-Tailed Woodstar
• Slender-tailed woodstar
• Slender tail hap
• Slendertail lanternshark
• Slender Tree-fern
• Slender Tree Fern
• Slender tree frog
• Slender Treefrog
• Slender Tree Shrew
• Slender treeshrew
• Slender Trefoil