Piper nigrum L. (Piperaceae) is widely distributed in the tropical and subtropical regions of the world. Pepper (fruits of P. nigrum) is one of the most popular spices in the world and has been also used as a folk medicine due to its many physiological activities, e.g., stimulation of the central nervous system, analgesic, and antipyretic activities. Phytochemical investigations of the fruits of this plant resulted in the isolation of 35 amides. However, very little is known on the chemical constituents of the roots of P. nigrum with only three amides reported. In our study, the root of P. nigrum was extracted with 70% MeOH. The residue was suspended in water and successively extracted with CHCl3, EtOAc, and n-BuOH. The CHCl3 fraction was found to increase amobarbital-induced sleeping time in mice. Phytochemical investigation of this fraction resulted in the isolation of seven new amides, N-isobutyl-4-hexanoyl-4-hydroxypyrrolidin-1-one (1), (±)-erythro-1-(1-oxo-4,5-dihydroxy-2E-decaenyl)piperidine (2), (±)-threo-1-(1-oxo-4,5-dihydroxy-2E-decaenyl)piperidine (3), (±)-threo-N-isobutyl-4,5-dihydroxy-2E-octaenamide (4), 1-(1,6-dioxo-2E,4E-decadienyl)piperidine (5), 1-[1-oxo-3(3,4-methylenedioxy-5-methoxyphenyl)-2Z-propenyl]piperidine (6), and 1-[1-oxo-5(3,4-methylenedioxyphenyl)-2Z,4E-pentadienyl]pyrrolidine (7), together with 32 known amides. Their structures were elucidated on the basis of spectroscopic analysis and chemical evidence.