GdCuSi has been studied by structural, magnetic, magneto-thermal, and magneto-transport measurements. The compound crystallizes in the Ni2In-type hexagonal structure. Magnetic measurements show antiferromagnetic ordering at T (N) = 14.2 K and a magnetic anomaly near 5 K, which are confirmed by different measurements. Magnetocaloric effect (MCE) has been estimated from both magnetization and heat capacity data and it shows a change in sign below T (N). Similar to MCE, magnetoresistance (MR) data also show sign change below T (N). The compound shows large MCE and MR near its ordering temperature. The sign change in MCE and MR is attributed to the non-collinear antiferromagnetic structure of the compound. The theoretical calculations suggest competition of ferromagnetic and antiferromagnetic interactions, which causes non-collinear magnetic structure in this compound.