This study considers the effect of a slanted side cooling wall that has varying inclination angles on the development of thermosolutal convection during the solidification of a supereutectic aqueous ammonium chloride (NH4Cl-H2O) solution. The shadowgraph and particle image velocimetry techniques were employed to observe the flow development and measure the flow velocity during solidification. The transient temperature distribution within the test cell was also measured by type-T thermocouples. Experimental results reveal that a more slanted side cooling wall accelerated the "filling-box" process, thus it could cause more serious A-segregates and material defects in the solidified ingot.