The classical biological control is a viable, effective approach to the management of alien invasive weeds. Recent criticisms of weed biological control have mainly centered on non-target impacts, the negative effects of biological control agents on species other than the targeted weed. These non-target impacts include both direct and indirect effects on native organisms due to changes in competition within trophic levels and changes in exploitation relationship between trophic levels in food webs. In this paper, we examined a wide range of weed biological control cases and discussed in detail the possible pathways to non-target impacts of biological control agents. In order to increase the ecological safety of weed biological control practices, we proposed to: (i) use imported natural enemies only as a last resort in fight against some of the most damaging exotic pests; (ii) consider only highly host-specific and highly effective biological control agents; (iii) conduct careful risk assessment of biological control agents before release, being particularly alert to their potential ecological impacts on non-target native organisms; and (iv) highly prioritize the need for taking ecology to the heart in biological control of weeds both in research and in application.