Self-assembling polycondensation was examined to prepare the whisker of poly(p-oxybenzoyl-alt-p-mereaptobenzoyl). Polymerizations were carried out in liquid paraffin (LPF) and aromatic solvents such as Therm S 800 and 1000 at 300 degreesC for 6 h. Polymerization concentration was 1.0 wt/vol %. The whisker was not obtained by the random copolymerization of p-acetoxybenzoic acid and S-acetyl-4-mercaptobenzoic acid at the molar ratio of 0.5 in feed. However, the whiskers were successfully prepared by the polymerization of S-(4-acetoxybenzoyl)-4-mercaptobenzoic acid (OS) and 4-(S-acetyl-4-mercaptobenzoyl)oxybenzoic acid (SO). The whisker prepared from OS (POS) in LPF was 18 mum in average length and 0.4 mum in average width, and that from SO (PSO) was slightly longer than POS. The whiskers prepared in aromatic solvents were much longer than those in LPF, for which the length was 36-49 mum. These whiskers consist of the alternating polymer chains, and the polymer chains align along the long axis of the whisker. The sequence regularity enhanced the crystallizability of the oligomers, and this led to the formation of whiskers. The oligomer formation rate was much higher than that of transesterfication reaction rate, and this large difference in these two rates made the oligomer precipitate with maintaining the alternating sequence. Further polymerization occurred in the crystals, and the whiskers having the alternating sequence were finally completed. The difference in the two rates increased with the decrease of the miscibility between the oligomer and the solvent, and therefore, OS and LPF were more advantageous to maintain the alternating sequence.