In organic chemistry, the cycloalkanes (also called naphthenes, but distinct from naphthalene) are the monocyclic saturated hydrocarbons. In other words, a cycloalkane consists only of hydrogen and carbon atoms arranged in a structure containing a single ring (possibly with side chains), and all of the carbon-carbon bonds are single. The larger cycloalkanes, with more than 20 carbon atoms are typically called cycloparaffins. All cycloalkanes are isomers of alkenes.

The cycloalkanes without side chains are classified as small (cyclopropane and cyclobutane), common (cyclopentane, cyclohexane, and cycloheptane), medium (cyclooctane through cyclotridecane), and large (all the rest).

Besides this standard definition by the International Union of Pure and Applied Chemistry (IUPAC), in some authors' usage the term cycloalkane includes also those saturated hydrocarbons that are polycyclic. In any case, the general form of the chemical formula for cycloalkanes is C_nH_2(n+1−r), where n is the number of carbon atoms and r is the number of rings. The simpler form for cycloalkanes with only one ring is C_nH_2n.