The plantlets of thyme were cultured on the 1/2 MS containing different sucrose,the NO₃^-/NH₄⁺,phenylalanine,glutamic acid and tyrosine,and were tested for the PAL activity.The PAL activities were also tested after the plantlets were induced for 0～120 h by MeJA,SA and chitosan at different culture times (20 d,30 d,40 d).The results showed that the highest PAL activity was obtained when the plantlets of thyme were cultured on the 1/2 MS medium with 2% sugar concentration and 2∶1 NO₃^-/NH₄⁺ ratio for 30 d.The PAL activities were increased to 126.3%,150.6% and 153.9% compared with CK by adding 0.6 mmol/L phenylalanine,0.8 mmol/L glutamic acid,and 0.4 mmol/L of tyrosine as precursor regulation,respectively.The PAL activities of plantlets cultured 20 d were increased 610.3％,788.1％ and 592.5％ than that of CK by adding 1.0 mmol/L MeJA,100 mg/L SA,and 200 mg/L chitosan as elicitors.The PAL activities of plantlets cultured 30 d were increased to 402.4％,541.2％ and 400.1％ compared with CK.And the highest PAL activities of plantlets cultured 40 d were increased to 390.2％,377.1％ and 413.4％ than that of CK.Therefore,the PAL activity was affected by adding different inducer at different culture time.