We investigated the thermoelectric properties of Ba₈Al₁₆Si₃₀ clathrate samples prepared by combining arc melting and spark plasma sintering methods under two different arc melting conditions. The x-ray diffraction, scanning electron microscopy, and energy dispersive analysis of x-ray studies indicate that Al composition is close to 15, which is higher than that of a single crystal reported, for both arc melting conditions. The carrier concentration of samples decreases to about 1×10²¹ cm^-3, which is lower than reported values so far in Ba₈Al₁₆Si₃₀ system. The Seebeck coefficient and the electrical conductivity alter slightly with the arc melting condition due to the slight difference in the carrier concentration. The lattice thermal conductivity (RT) is as low as about 1.3 Wm^-1K^-1, which is comparable to Bi₂Te₃-based bulk alloy, independently of the arc melting condition. The thermoelectric figure of merit ZT is about 0.4 at 900 K. An estimation indicates that ZT reaches 0.8 (1200 K) at the optimum carrier concentration of about 3×10²⁰ cm^-3 in Ba₈Al₁₆Si₃₀ system.