Sa-So
- Joseph Sabine (1770–1837), English naturalist
- Julius von Sachs (1832–1897), German botanist
- Étienne Geoffroy Saint-Hilaire (1772–1844), French naturalist
- Isidore Geoffroy Saint-Hilaire (1805–1861), French zoologist
- Carl Ulisses von Salis-Marschlins (1762–1818), Swiss naturalist interested in botany, entomology, and conchology
- Edward James Salisbury (1886–1978), British botanist
- Richard Anthony Salisbury (1761–1829), British botanist
- Jonas Salk (1914–1995), American biologist, inventor of polio vaccine
- Robert Sapolsky (born 1957), American neuroscientist
- Georg Ossian Sars (1837–1927), Norwegian marine biologist
- Michael Sars (1809–1869), Norwegian taxonomist
- William Saunders (1822–1900), American botanist
- Horace-Bénédict de Saussure (1740–1799), Swiss naturalist
- Marie Jules César Savigny (1777–1851), French zoologist
- Thomas Say (1787–1843), American naturalist
- George Schaller (born 1933), American zoologist, widely considered the preeminent field biologist of the 20th century
- Friedrich Schlechter (1872–1925), German botanist
- Hermann Schlegel (1804–1884), German ornithologist
- Matthias Jakob Schleiden (1804–1881), German co-founder of the cell theory
- George Schoener (1864–1941), German-American botanist
- Johann David Schoepf (1752–1800), German botanist and zoologist
- Heinrich Wilhelm Schott (1794–1865), German botanist
- Johann Christian Daniel von Schreber (1739–1810), German naturalist
- Leopold von Schrenck (1826–1894), Russo-German zoologist
- Charles Schuchert (1858–1942), paleontologist
- Theodor Schwann (1810–1882), German physiologist
- Georg August Schweinfurth (1836–1925), German botanist
- Philip Sclater (1829–1913), English zoologist
- Giovanni Antonio Scopoli (1723–1788), Italian-Austrian naturalist
- Henry Seebohm (1832–1895), English ornithologist
- Prideaux John Selby (1788–1867), English botanist and ornithologist
- Nikolai Alekseevich Severtzov (1827–1885), Russian naturalist
- Richard Bowdler Sharpe (1847–1909), English zoologist
- George Shaw (1751–1813), English botanist and zoologist
- Rupert Sheldrake (born 1942), biologist
- George Ernest Shelley (1840–1910), English ornithologist
- Sir Charles Scott Sherrington (1857–1922), British physiologist and neuroscientist, winner of the 1932 Nobel Prize in Physiology or Medicine for his research on neurons
- Philipp Franz von Siebold (1796–1866), German botanist
- George Gaylord Simpson (1902–1984), American paleontologist
- Rolf Singer (1906–1994), German born mycologist
- John Kunkel Small (1869–1938), American botanist (abbr. in botany: Small)
- Andrew Smith (1797–1872), Scottish zoologist
- Edgar Albert Smith (1847–1916), British zoologist and conchologist
- Frederick Smith (1805–1879), British entomologist
- James Edward Smith (1759–1828), English botanist (abbr. in botany: Sm.)
- Johannes Jacobus Smith (1867–1947), Dutch botanist (abbr. in botany: J.J.Sm.)
- James Leonard Brierley Smith (1897–1968), South African ichthyologist
- John Maynard Smith (1920–2004), biologist
- John Otterbein Snyder (1867–1943), American zoologist
- Solomon H. Snyder (born 1938), American neuroscientist, co-discovered endorphins
- Daniel Solander (1733–1782), Swedish botanist
- Louis François Auguste Souleyet (1811–1852), French zoologist
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