The present study describes chemical composition, antioxidant, antibacterial, allelopathic and insecti-cidal properties of essential oil of Thymus algeriensis (Lamiaceae), a North African endemic species. The essential oil from all organs of T. algeriensis were extracted by hydrodistillation and analysed by gas chromatography (GC) and gas chromatography-mass spectrometry (GC–MS). A high variation among organs for the majority of compounds was shown. Caryophyllene oxide (21.1%) and veridiflorol (17.2%) were the main constituents in roots, while elemol (10.2%) and caryophyllene oxide (17.8%) were identified as the main constituents for stems. Leaves were characterized by high levels of-pinene (19.5%), 1,8-cineole (11.6%) and camphor (10.4%). Based on the determination of the diameter of inhibition and the determination of the minimum inhibitory concentration, a moderate to high antibacterial activity according to oils was revealed against five bacteria strains. However, oils from Dj. Jdidi locality showed higher bactericidal effect (MICs = 1–3.25 l/ml) than those from other samples. The level of antioxidant activity estimated by DPPH (IC 50 = 4.31–9.23 mg/ml) and ABTS (11.69–28.23 gTE/mg DW) test was moderate. The obtained results also showed that the leaf oils inhibited the shoot and root growth of Medicago sativa and Triticum aestivum seedlings. Thus, the T. algeriensis oils may be used as a natural herbicide. Furthermore , these oils were found to possess strong insecticidal activity (LC 50 = 44.25–112.75 l/l air) against cotton leafworm larvae. Thus, the essential oil of this plant could be used as a potential source of natural antioxidants and bioactive molecules in pharmaceutical as well as in food industries.