<jats:title>Abstract</jats:title><jats:p>A new limonoid, 7‐<jats:italic>O</jats:italic>‐acetyl‐7‐<jats:italic>O</jats:italic>‐debenzoyl‐22‐hydroxy‐21‐methoxylimocinin (<jats:bold>2</jats:bold>), and two new flavonoids, 3′‐(3‐hydroxy‐3‐methylbutyl)naringenin (<jats:bold>7</jats:bold>) and 4′‐<jats:italic>O</jats:italic>‐methyllespedezaflavanone C (<jats:bold>9</jats:bold>), along with nine known compounds, including two limonoids, <jats:bold>1</jats:bold> and <jats:bold>3</jats:bold>, and seven flavonoids, <jats:bold>4</jats:bold>–<jats:bold>6, 8</jats:bold>, and <jats:bold>10</jats:bold>–<jats:bold>12</jats:bold>, were isolated from a MeOH extract of the flowers of <jats:italic>Azadirachta indica</jats:italic> A.<jats:sc>Juss.</jats:sc> var<jats:italic>. siamensis</jats:italic> <jats:sc>Valeton</jats:sc> (Siamese neem tree; Meliaceae). The structures of new compounds were elucidated on the basis of extensive spectroscopic analysis and comparison with literature data. All of these compounds were evaluated for their melanogenesis‐inhibitory activities in B16 melanoma cells induced with <jats:italic>α</jats:italic>‐melanocyte‐stimulating hormone (<jats:italic>α</jats:italic>‐MSH). Compound <jats:bold>2</jats:bold> (16.9% melanin content at 30 μ<jats:sc>M</jats:sc>), 6‐deacetylnimbin (<jats:bold>3</jats:bold>; 49.6% melanin content at 100 μ<jats:sc>M</jats:sc>), and kaempferide (<jats:bold>10</jats:bold>; 41.7% melanin content at 10 μ<jats:sc>M</jats:sc>) exhibited inhibitory effects with no, or almost no, toxicity to the cells (81.0–111.7% cell viability). In addition, evaluation of their cytotoxic activities against HL60, A549, AZ521, and SK‐BR‐3 human cancer cell lines, isoazadironolide (<jats:bold>1</jats:bold>), 4′‐<jats:italic>O</jats:italic>‐methyl‐8‐prenylnaringenin (<jats:bold>5</jats:bold>), euchrestaflavanone A (<jats:bold>8</jats:bold>), <jats:bold>9</jats:bold>, and 3‐methoxy‐3′‐prenylnaringenin (<jats:bold>12</jats:bold>) revealed potent cytotoxicities against one or more cell lines with <jats:italic>IC</jats:italic><jats:sub>50</jats:sub> values in the range of 4.5–9.9 μ<jats:sc>M</jats:sc>.