Effects of growth substrate and nucleic acid reduction in the production of bacterial protein meal (BPM) were studied using a bacteria culture containing mainly Methylococcus capsulatus (Bath). BPM were produced on natural gas (>90% methane) (BPMG), methanol (BPMM), or methanol followed by nucleic acid reduction (BPMM-NAR). BPMG and BPMM had similar crude protein (CP) and amino acid contents, whereas BPMM-NAR had slightly higher CP and amino acid contents. Digestibility of CP and amino acids in mink was higher for BPMM than for BPMG. Tryptophan revealed the greatest difference in true digestibility (70.5% for BPMG vs 89.5% for BPMM) and lysine the least difference (93.2% for BPMG and 95.7% for BPMM). There were no differences in CP or amino acid digestibility between BPMM and BPMM-NAR. It was concluded that BPM grown on methanol gave higher digestibility of CP and amino acids than natural gas, probably due to lower proportion of bacterial intracellular membrane protein.