A primary cDNA library with a size of 1.34 x 10(6) PFU was constructed from Haemaphysalis qinghaiensis eggs and was immunoscreened with rabbit anti-H. qinghaiensis serum. One clone (Hq22, named following those clones obtained from adult Haemaphysalis qinghaiensis cDNA library which we constructed before) screened from the cDNA library was selected randomly for sequencing. The entire sequence of the clone was subsequently obtained using rapid amplification of the cDNA ends (RACE). A search of the cloned sequence against GenBank revealed that it related to ribosomal protein L23a (Rpl23a) and had a high percentage similarity to this protein from different species. Conserved domains for Rpl23a were also identified in the cloned sequence. Expression analysis by RT-PCR showed that this gene is expressed in salivary glands, midguts, other tissues and different developmental stages of H. qinghaiensis. Based on the H. qinghaiensis Rpl23a sequence, open reading frames (ORF) of Rpl23a of Heamaphysalis longicornis and Boophilus microplus were also cloned and were performed for comparison with Rpl23a of H. qinghaiensis and other organisms as well. Vaccine based on Rpl23a recombinant protein cannot protect sheep against H. qinghaiensis.