This study investigated the reinforced concrete beams’ structural behavior when the sand aggregate is partially replaced with coconut peat also known as cocopeat. The concrete mixes were prepared by 0, 20, 50 and 100 % variation levels of replacement. Flexural loading tests were conducted on the reinforced concrete beams by also considering the variations in stirrup spacing and main bar diameters. The results indicated that, replacement up to 20 % of sand with hardened cocopeat maintained acceptable structural performance with those with 20 % replacement presented a comparable load bearing capacity and crack resistance to control specimen. Greater than 20 % replacement level exhibited significant reduction in strength and stiffness. The results also revealed that closer stirrup spacing, and larger diameter steel bars overcome the limitations of cocopeat content, improving the beam performance. The study supports the potential use of cocopeat as partial sand replacement in sustainable concrete construction.