Abstract: Authors investigated the effects of the extract from Camellia semiserrata Chi oil residua with ethanol on development of citrus blue and green mold diseases caused by Penicillium italicum and P. digitatum. In vitro antimicrobial experiments revealed that the crude extract could inhibit the growth of P. italicum and P. digitatum. Concentration at 10 mg/mL and above gave rise to 100% and 70% inhibition againstP. italicum and P. digitatum, respectively, while tea saponin at the same concentration only 30% and 58%, respectively. Treatment with the crude extract of lemon and Shatang mandarin fruits inoculated by P. italicum suppressed blue mold disease lesion development and disease incidence. Compared to water control, the inhibited rate of lesion development was 60% and above, and disease incidence decreased by 25%—58% at 50 mg/mL extract. This research showed that theextract was much better than tea saponin in controlling P. italicum and P. digitatum growth and in vivo disease development, indicating other active antifungal components existing in the crude extract of Camellia semiserrata Chi oil residua.