The thirteenth part of the OGLE-III Catalog of Variable Stars (OIII-CVS) contains 19 384 long-period variables (LPVs) detected in the Small Magellanic Cloud. The sample is composed of 352 Mira stars, 2222 semiregular variables (SRVs) and 16810 OGLE Small Amplitude Red Giants (OSARGs). Sources are divided into oxygen-rich and carbon-rich stars. The catalog includes time-series V/ photometry obtained between 1997 and 2009. Methods used to select and classify variable stars are described. We show some statistical prop-erties of the sample, and compare it with LPVs in the Large Magellanic Cloud. Additionally, we present objects of particular interest, e.g., a SRV with outbursts, and a Mira star with the longest known pulsation period P = 1860 days.