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- George Emil Palade (born 1912), Romanian-American biologist, discoverer of ribosomes, Nobel Prize
- Paul Maurice Pallary (1869–1942), French-Algerian malacologist
- Peter Simon Pallas (1741–1811), Russian zoologist
- Edward Palmer (1829–1911), British botanist
- Josif Pancic (1814–1888), Serbian botanist
- Paracelsus (1493–1541), German alchemist
- Louis Pasteur (1822–1895), French biochemist
- William Paterson (1755–1810), British botanist and explorer
- Robert Patterson (1802–1872), Irish naturalist
- Daniel Pauly (born 1946), French marine biologist
- Ivan Pavlov (1849–1936), Russian physiologist, psychologist and physician, discovered conditioning, won the Nobel Prize for his research on the digestive system
- Titian Peale (1799–1885), American naturalist
- Donald C. Peattie (1898–1964), American botanist
- Paul Pelseneer (1863–1945), Belgian malacologist
- Jean-Marie Pelt (born 1933), French botanist
- Thomas Pennant (1726–1798), Welsh naturalist and antiquary
- Henri Perrier de la Bâthie (1873–1958), French botanist
- George Perry (naturalist), 19th century English naturalist
- Christian Hendrik Persoon (1761–1836), biologist
- Paul Petard (1912–1980), French botanist
- Wilhelm Peters (1815–1883), German naturalist
- Ludwig Karl Georg Pfeiffer, German physician, botanist and conchologist
- Rodolfo Amando Philippi (1808–1904), German-Chilean zoologist
- Constantine John Phipps (1744–1792), English explorer
- David Andrew Phoenix, (born 1966), Biochemist
- Frederick Octavius Pickard-Cambridge (1860–?), English entomologist
- Octavius Pickard-Cambridge (1828–1917), English entomologist, uncle of above
- Charles Pickering (1805–1878), American naturalist
- Cándido Bolívar Pieltain (1897–1976), Spanish naturalist
- Henry Augustus Pilsbry (1862–1957), American zoologist, malacologist
- Gregory Goodwin Pincus (1903–1967), American biologist and co-inventor of the contraceptive pill
- Ronald Plasterk, (born 1957), Dutch molecular biologist, columnist and politician
- Pliny the Elder (23–79), Roman natural philosopher
- Reginald Innes Pocock (1863–1947), British taxonomist (mammals and arachnids)
- Felipe Poey (1799–1891), Cuban zoologist
- Joel Roberts Poinsett (1779–1851), American botanist
- Giuseppe Saverio Poli (1746–1825), Italian physicist, biologist and natural historian
- Winston Ponder, Australian malacologist
- Arthur William Baden Powell (1901–1987), New Zealand malacologist and paleontologist
- Thomas Littleton Powys, 4th Baron Lilford (1833–1896), English ornithologist
- Karel Presl (1794–1852), Bohemian botanist
- Alice Pruvot-Fol (1873–1972), French malacologist
- Jan Evangelista Purkyně (1787–1869), Czech anatomist and physiologist
- Frederick Traugott Pursh (1774–1820), German-American botanist
- Paul Émile de Puydt (1810–1888), Belgian botanist
- Nikolai Przhevalsky (1839–1888), Russian explorer
Read more about this topic: List Of Biologists