The present invention provides a co-condensate containing a structural unit derived from p-tert-butylphenol, a structural unit derived from o-phenylphenol, and a structural unit derived from resorcin, and having a softening point of 150° C. or lower; a method for producing the co-condensate including reacting a mixture of p-tert-butylphenol and o-phenylphenol with formaldehyde in the presence of an alkali, and then reacting resorcin in a 0.8-fold molar amount or more relative to a total amount of p-tert-butylphenol and o-phenylphenol; and a rubber composition containing the co-condensate.