Five 9-fluorenone derivatives, 2-amino-, 2-hydroxy-, 2-nitro-, and 2,4,7-trinitro-9-fluorenone (AF, HF, NF, and TNF, respectively), and 2,4,7-trinitro-9-fluorenylidenemalononitrile (TNFM), were vacuum evaporated onto the electrochemically prepared poly(3-methylthiophene) (PMeT) film to fabricate the organic two-layer diodes Au/PMeT/9-fluorenones/Al, which exhibited a normal rectification and an anomalous conduction effect. The conduction behavior in the "forward bias direction" appear to be similar for all the derivatives used. The major difference occurred in the "reverse bias direction". Normal rectification effect was observed for NF and HF diodes : a very small backward current was observed when the gold electrode was negatively biased with respect to the aluminum electrode. On the other hand, an anomalous conduction effect was observed for TNF and TNFM diodes : a significantly larger backward current was observed when the gold electrode was negatively biased with respect to the aluminum electrode. A new type of mechanism for the control of the electron transfer direction in organic two-layer diodes is proposed from the viewpoint of redox properties of the compounds studied.