A masterbatch manufacturing method comprises an operation in which rubber latex and a carbon black slurry containing a compound according to Formula (I), below, are mixed. At Formula (I), R1 and R2 each indicates a hydrogen atom, an alkyl group having 1 to 20 carbons, an alkenyl group having 1 to 20 carbons, or an alkynyl group having 1 to 20 carbons. R1 and R2 may be the same or different. M+ indicates sodium ion, potassium ion, or lithium ion.