Sexual selection causes reproductive interference (RI) through male harm and female resistance. Larval resource competition (RC) promotes sexual selection by adult body size increases.  Here we predicted that larval RC would alter RI intensity.  To test this prediction, we established four evolutionary experimental lines using Callosobruchus maculatus.  Experimental lines consist of a combination of two larval RC regimes (contest and scramble competition: C and S) and two adult mating regimes (polygamy and monogamy: P and M).  We measured C-value that describes the proportion of the contest type in the population, elytra length as adult body size, and fecundity in two remating treatments with no male (NOM) and a C. chinensis male (HET).  We also calculated RI intensity using fecundity in NOM and HET treatments.  As expected, C lines and P lines had higher RI intensity than S lines and M lines, respectively.  Moreover, we analyzed within- and between-generation effects from larval RC to RI using structural equation modeling (SEM).  The SEM result revealed that larval RC has causal effects on RI intensity via adult body size both within and between generations.