A riser clamp (1) has two opposed clamp halves (2, 3), each of said clamp halves (2, 3) having a semicircular section (21,31) opposing the semicircular section of the other clamp half for surrounding a riser pipe. Each of said clamp halves has at the ends of its semicircular section radially extending clamp flanges (22, 32) to be clamped against the corresponding opposing clamp flanges of the other clamp half. The riser clamp (1) is in use supported from beneath by a support surface. At least one of two opposing clamp flanges is provided with an isolation member (4) comprising a resilient support strip (41), which support strip (41) is located below the corresponding clamp flange for resiliency supporting it. The isolation member (4) further comprises at least one web (42) extending upwardly from the support strip (41) along the corresponding clamp flange, wherein said web (42) is attached to the corresponding clamp flange.