In the SBR latex as the compounding agent of portland cement mortar, many kinds of minor components besides SBR polymer were generally involves; they are, for example, surface active agents, antiforming agents, and polymerization modifier, etc. In this paper, the separation of these substances by the solvent extraction method and the analysis by infra-red spectrophotometric method were described. Surface active agents (polyoxyethylene alkyl ether and alkylbenzene sulfonate) were separated by the methyl alcohol extraction and antiforming agents (silicone) by the carbon. tetrachroride extraction. On the other hand, polymerization modifier (quinone derivatives) was separated as a precipitate from the solution of the methyl alcohol extraction by keeping it for 2 days at room tempreature. Only silicone was determined from the rate of the absorption intensity of 800 cm^-1(silicone) and 840 cm^-1 (SBR).