Abstract. Wamuyu KR, Machocho AK, Wafula AW. 2020. Antimicrobial and phytochemical screening of Lannea schweinfurthii (Engl.) Engl. Bioteknologi 17: 1-13. Phytochemicals are currently receiving more attention because of their effectiveness in the treatment of infectious diseases as well as mitigating various side effects caused by conventional antimicrobials. Pharmacological studies of Lannea schweinfurthii (Engl.) Engl. has reported antimicrobial property of the plant, but the active ingredients in the plant are largely understudied. Here, we collected the stem bark of L. schweinfurthii (Engl.) Engl., then grounded into a fine powder. Sequential extraction was conducted with hexane, dichloromethane (DCM), ethyl acetate (EtOAc), and methanol (MeOH). The crude extracts were examined for bioassay screening for their antibacterial activity against Gram-positive Staphylococcus aureus and Bacillus subtillis and Gram-negative Pseudomonas aeruginosa and Escherichia coli and antifungal activities against Candida albicans. The EtOAc and MeOH crude extracts showed moderate and high activities, ranging from 11 to 21 mm inhibition zones against the microbes used except P. aeruginosa. Hexane and DCM crude extracts showed a mild activity of 7 mm. Tetracycline and nystatin were applied as positive controls for bacteria and fungi, respectively, exhibited inhibition zones of 18 mm. The GC-MS analysis was carried out on the crude DCM, and MeOH extracts to give a preliminary hint of the class of compounds. The spectral data obtained from the crude extracts of DCM and MeOH indicated the presence of phenolic compounds, fatty acids, and their derivatives, polyketide derivatives, terpenoids, and steroids in the plant. Purification of crude extracts was performed using solvent partition and chromatography: CC, VLC, and PTLC. Structural elucidation and characterization were done using standard spectroscopic methods. The combined hexane/DCM extract produced two compounds, namely; 3-(10'-tridecenyl) phenol (LS01) and di-(2’-ethylhexyl) ester phthalic acid (LS05). The extract of ethyl acetate yields three compounds, namely lupeol (LS02), β-sitosterol (LS03), and epicatechin (LS04). Bioassay of the isolated compounds showed that epicatechin had high activity against the S. aureus and B. subtillis and Gram-negative E. coli. Furthermore, epicatechin showed an activity of 14 mm against C. albicans. Here, we showed that the stem bark of L. schweinfurthii has bioactive chemical constituents. Further studies such as cytotoxicity tests should be done both on the crude extracts and isolated compounds to ascertain reported activity to use bioactive components either as antimicrobials or as templates in drug synthesis. On the other hand, measures should be put in place to conserve the plant species from extinction.