Dynorphin A-(1-13) (I) and its two analogs were synthesized by solid-phase method. Fully-protected peptides were cleaved from the resin with HF. The three products were purified and their analgesic activity (antiwrithing response in mouse) and receptor affinity in mouse vas deferens (MVD) and rabbit vas deferens (RVD) were measured. The biological and pharmacological results showed that the replacement of Gla2, Ile8 and Pro10 by D-Ala8 and D-Pro10 caused an increase in analgesic activity, receptor affinity and selectivity. In analgesia and RVD assay, its activity is 2.6 times and 135 times respectively higher than dynorphin A-(1-13). The structure-activity relationships were briefly discussed.