This field study was conducted to investigate the effect of humic acid on microbial and the activities of three enzymes in the soil where gingers (Zingiber officinale Rose) were grown. Soil was subjected to four fertilizer regimes: control, humic acid only (19.6g/m2), inorganic nutrient (45.0 g N/m2, 15.0 g P2O5/m2, and 60.0 g K2O/m2), and humic acid compound (45.0 g N/m2, 15.0 g P2O5/m2, 60.0 g K2O/m2 and 19.6g humic acid/m2). Microbial carbon level was greater during the early experimental period, but lower during the late experimental period in humic acid only versus the control and in humic acid compound versus nutrient treatment. Urease activity level was lower during the early experimental period, but greater during the late experimental period in humic acid only versus the control and in humic acid compound versus nutrient treatment. When data were averaged over the entire experimental period, humic acid only treated soil exhibited a 17.3% higher active microbial carbon level, 11.4% higher acid phosphatase activity, and 10.6% lower invertase activity. than the control. Soil treated with the humic acid compound had 18.6% higher active microbial carbon level, 10.1% higher acid phosphatase activity and 7.6% higher invertase activity than inorganic nutrient treatment, when data were averaged over the entire experimental period.