Sugarcane bagasse ash sand (SBAS), a by-product of sugar and ethanol industries, can be used as a partial replacement of natural sand in production of eco-efficient concrete and mortars. Due to its finer particles, incorporation of SBAS results in refinement of pores in cementitious composites. This in turn leads to greater cracking susceptibility triggered by self-desiccation processes in autogenous shrinkage. To mitigate this problem, superabsorbent polymers (SAP) can be used as internal curing agents. This study aims to evaluate autogenous shrinkage and mechanical properties of cementitious composites with SBAS modified by SAP. Mortars were produced with 30% SBAS, and three types of SAP with different water absorption capacities. The results indicate high efficiency of SAP in controlling water supply for cement hydration, reducing autogenous shrinkage by up to 67% in relation to the reference mixture without SAP and SBAS. Flexural and compressive strengths were not significantly affected by SAP when compared to the reference samples. Therefore, application of SAP in such composites could notably improve durability of eco-efficient concretes.