Three new compounds, i.e. 1-[2-(5-hydroxymethyl-1H-pyrrole-2-carbaldehyde-1-yl) ethyl]-1H-pyrazole (1), 1-({[5-(alpha-D-galactopyranosyloxy) methyl]-1H-pyrrole-2-carbaldehyde-1-yl}-ethyl)-1H-pyrazole (2), and (4-hydroxyphenyl) methanol 4-[beta-D-apiofuranosyl(1 -> 2)-O-b-D-glucopyranoside] (3), were isolated from an extract of watermelon seeds. Compounds 1 and 2 were pyrazole-alkaloids with a pyrrole ring. This is the first study to show compounds with pyrrole and pyrazole rings in a molecule isolated from natural products. In the evaluation for melanogenesis inhibitory, compound 1 exhibited modest inhibitory activity on melanogenesis without cytotoxicity. Meanwhile compound 2 showed some inhibitory activity accompanied by some cytotoxicity. (C) 2015 Phytochemical Society of Europe. Published by Elsevier B.V. All rights reserved.