The concept of sustainability has gradually expanded within engineering fields, mainly due to its role in conserving natural raw materials by replacing them with recycled materials. One practical example is the replacement of natural aggregate with recycled concrete aggregate (RCA) in rigid pavements, which helps reduce waste. However, the performance of RCA under varying environmental conditions remains unclear and requires extensive research. The study aims to examine the effect of external sulfate attack on concrete mixes containing different proportions of recycled concrete aggregate and silica fume. This study partially replaced natural coarse aggregate with recycled coarse aggregate at ratios of 50%, 75%, and 100%, and cement was partially replaced with 10% silica fume. Four mixes were prepared, including a Control mix (C), (A1) mix, (A2) mix, and (A3) mix. Workability was measured through a slump test, followed by casting 48 cubes with dimensions of 15 cm. Half of the cubes (24) were immersed in water, while the other half were placed in water and 5% magnesium sulfate solution for 28 and 120 days. Density and compressive strength tests were conducted on all samples at these curing durations. The study compared the results of samples immersed in water with those submerged in the water and magnesium sulfate solution to determine the degree of sulfate impact. Results showed that silica fume positively affected sulfate resistance and significantly improved RCA mixes in the later ages. Nonetheless, the control mixes exhibited greater strength than the RCA mixes., particularly the (A3) mix. The role of silica fume was evident from the results, and the study also highlighted the performance of recycled aggregate under external sulfate attack in specific terms.