In search of bioactive substances from Mexican marine organisms, crude ethanol-extract from the marine alga Codium amplivesiculatum was fractionated in chromatographic columns of silica gel at 60 Å (230-400 mesh) using solvent mixtures of increasing polarity. All the fractions were submitted to antibacterial assays. The major metabolite from an anti-tuberculosis fraction (MIC = 100 μg mL–1) was purified and identified as 1-octodecanol (1). The anti-tuberculosis activity was attributed to 1 with bases in previous reports. In addition, clerosterol (2) was obtained by crystallization from an active fraction against Staphylococcus aureus and Vibrio parahaemolyticus (MIC = 125 and 250 μg mL–1, respectively). Both structures were established by interpretation and comparison of infrared and 1H NMR spectroscopic data. In contrast with other studies, 2 showed a non-significant cytotoxicity against the cell line PC-3 (% GI = 21.05 ± 0.3 at 50 μg mL–1). To our knowledge, these metabolites are reported for the first time from C. amplivesiculatum, and this is one of very rare reports of saturated long-chain alcohols isolated from chlorophytes.