Sincerus may refer to:
The Latin word for sincere or:
People
Sincerus, Roman Catholic Bishopric of Amelia in the fifth century
Pseudonyms
Samuel Adams (1722-1803) American statesman
Elias Schwarzfeld (1855–1915), Moldavian and later Romanian Jewish historian, essayist, novelist and newspaperman who wrote as Edmond Sincerus Karl-August von Reisach (1800–1869), German Catholic theologian and Cardinal who wrote under Augusts Sincerus Sigmund Richter, a probable progenitor of the Order of the Golden and Rosy Cross who used the name Sincerus Renatus Peter Joseph Elvenich (1796–1886), German Catholic theologian and philosopher who wrote under Sincerus Pacificus Georg Ludwig Oeder, theologian and father of Georg Christian Oeder, who used the pseudonym Sincerus Pistophilus