Experiments have been performed to enhance negative thermal expansion (NTE) in the La(Fe,Co,Si)(13)-based compounds by optimizing the chemical composition, i.e., proper substitution of La by magnetic element Pr. It is found that increasing the absolute value of the average coefficient of thermal expansion (CTE) in the NTE temperature region (200-300 K) attributes to enhancement of the spontaneous magnetization and its growth rate with increasing Pr content. Typically, the average CTE of La1-xPrxFe10.7Co0.8Si1.5 with x = 0.5 reaches as large as -38.5 X 10(-6) K-1 between 200 and 300 K (Delta T = 100 K), which is 18.5% larger than that of x = 0. The present results highlight the potential applications of La(Fe,Co,Si)(13)-based compounds with a larger NTE coefficient.