The main objectives of this study were to evaluate the effect of animal manures combinations and humic acid on some soil biochemical properties. The laboratory incubation experiment was conducted using a completely randomized design with three replicates. The animal manures included chicken manure (ChM) and cow manure (CoM). The treatments of humic acid (HA), chicken manure (ChM) and cow manure (CoM) were applied on clay soil at a rate of 10 t. ha-1. The treatments used were: Control (T1), HA (T2), HA + ChM (T3) and HA + CoM (T4). The soil samples were incubated for 15, 30, 45 and 60 days at 28 ˚C and was analyzed for soil pH, the electrical conductivity (EC), total nitrogen, available phosphorus, potassium content, soil organic carbon percentages (SOC) and soil respiration (CO2). In general, the results showed a significant difference between all treatments and the control. Also, the applications of treatments have lowered the soil pH and significant increase in EC was observed as days of incubation. While, the N, P, K, SOC and soil respiration (CO2) were significant increased and reached its peak at 45 days of incubation and decreased thereafter with time. The results showed that applications of organic matter had significant effect on soil biochemical properties and treatment 4 T4 (HA+ CoM) showed a significant superiority compare with other treatments.