9-Nitrocamptothecin (9-NC) is an orally administered topoisomerase-I inhibitor for the treatment of pancreatic carcinoma, but its oral absorption and bioavailability are poor. The main objective of this study was to develop optimal 9-nitrocamptothecin (9-NC) microemulsion prepared by self-microemulsifying drug delivery system (SMEDDS). Two SMEDDS formulations of 9-NC prepared from a mixture of ethyl oleate, Tween-80 (T-form) or Cremophor EL (C-form), and PEG-400/ethanol were formed as microemulsions under dilution with aqueous phase. The resulting microemulsions were evaluated in vitro and in vivo, including the kinetics and antitumor effects in SKOV-3 human ovarian cancer xenograft in nude mice. Following 1:10 aqueous dilution of optimal 9-NC SMEDDS, the droplet sizes of resulting microemulsions were (30.8+/-4.6)nm and (39.8+/-8.2)nm for SMEDDS T-form and C-form, respectively, and the zeta potential values were -(4.3+/-0.5)mV and -(5.7+/-0.5)mV, respectively. In SKOV-3 cells, the growth inhibition (IC50) of various 9-NC formulations was greatest with SMEDDS T-form (3.5+/-0.7 nM) followed by SMEDDS C-form (4.6+/-0.4 nM), 9-NC solution (6.6+/-1.4 nM) and 9-NC suspension (26.0+/-2.9 nM) (P<0.01). It was indicated that the area under the plasma concentration-time curve (AUC0-->8h) values of various formulations of 9-NC after oral administration ranked as the following sequence: SMEDDS T-form (360.12+/-19.44 ngh/ml) approximately SMEDDS C-form (351.71+/-33.66 ngh/ml) >9-NC solution (241.21+/-24.67 ngh/ml)>9-NC suspension (161.24+/-24.31 ngh/ml). The 9-NC SMEDDS formulations also produced significantly more tumor shrinkage (P<0.01) when compared to 9-NC suspension in nude mice bearing human ovarian cancer xenografts. The results suggest that SMEDDS is a promising drug delivery system to increase the oral bioavailability and antitumor effects of 9-NC and may be applied to other lipophilic drugs. 9-NC SMEDDS represents a novel 9-NC therapy for cancer patients.