Provided are monospecific and bispecific proteins that bind specifically to OX40 and/or PD-L1. Exemplary proteins release the inhibition through PD-L1 and stimulate T cell through OX40. Exemplary polyvalent proteins comprise at least one OX40 binding site and at least one PD-L1 binding site. In certain embodiments, the binding sites may be linked through an immunoglobulin constant region. Anti-OX40 and anti-PD-L1 antibodies are also provided.