The present invention provides a prophylactic and/or therapeutic agent for pulmonary hypertension, comprising an antagonistic mutein of MCP-1 or a salt thereof, a DNA molecule comprising a nucleotide sequence encoding the antagonistic mutein of MCP-1, or a neutralizing antibody against MCP-1. The antagonistic mutein of MCP-1 or a salt thereof, the DNA molecule having a nucleotide sequence encoding the antagonistic mutein of MCP-1, or the neutralizing antibody against MCP-1 has hypotensive activity, and thus is useful as a pharmaceutical agent for preventing and/or treating pulmonary hypertension (primary pulmonary hypertension, in particular).