Alexander Williamson may refer to:
- Alexander William Williamson (1824–1904), chemist who discovered the Williamson ether synthesis reaction
- Alexander Williamson (missionary) (1829–1890), Scottish Protestant missionary to China with the London Missionary Society
- Alexander Watt Williamson (1849–1928), New Zealand schoolteacher
- Alexander Williamson (colonial administrator) from 1897 Diamond Jubilee Honours