Concrete is a construction material used in almost all buildings. This study aimed to find out the flexural strength of concrete using Serayu river sand and using milled stone sand of Serayu river. The sample used was in the form of blocks with a size of 15 cm x 15 cm x 60 cm with a total of 4 samples, namely 2 samples from Serayu sand and 2 samples from the milled stone sand of Serayu river. This test sample was tested when the concrete was 28 days old without conversion. The result of the study of Serayu river sand with a slump value of 3.74% was at 2.8122 Mpa. The result of the study of Serayu Milled Stone Sand with a slump value of 2.88% was at 3.27MPa. Based on the results, it is proven that the milled stone of the Serayu river is more resilient than the sand of
the river.