Models of the evolution of sexual cannibalism argue that males may offset the cost of cannibalism if materials of their soma are allocated to the eggs that they might father. We studied male reproductive investment via sexual cannibalism in the praying mantid Tenodera sinensis. Males and females were each fed differently radiolabeled crickets (Acheta domesticus) and allowed to mate. We allowed half of the pairs to progress to sexual cannibalism and prevented cannibalism in the other half. We assess the relative allocation of both male-derived somatic materials and ejaculate materials into the eggs and soma of the female. Our results show that male somatic investment offsets female investment in offspring. Eggs and reproductive tissues of females that cannibalized their mates contained significantly more male-derived amino acids. There was also a marginally nonsignificant increase in eggs produced subsequent to sexual cannibalism. Sexual cannibalism thus increases male material investment in offspring. We also show that males provide substantial investment via the ejaculate, with males passing 25.1% of their radiolabeled amino acids to females via the ejaculate even in the absence of cannibalism.