A new quinoline alkaloid named helietidine ( 1), and seven known compounds ( 2 - 8) have been isolated from the stem barks of Helietta longifoliata. The structures of the new and the known compounds were established on the basis of spectral evidence, especially by 2D NMR ( 1H- 1H COSY, NOESY, HMQC, HMBC). In addition, the volatile constituents of H. longifoliata leaves were analysed by gas chromatography-mass spectrometry (GC-MS). Twenty-five constituents were identified representing ca. of 96 % of the oil, and limonene (17.50 %), germacrene D (16.60 %), elemol (11.81 %), bicyclogermacrene (11.67 %), guaiol (11.53), and epi-alpha-bisabolol (7.24 %) were the most abundant components. The oil was bioactive against some Gram-positive and Gram-negative bacteria, as revealed by bioautography.