The purpose of this study was to evaluate the response of rubber tree [Hevea brasiliensis(Willd. ex Adr. de Juss) Muell. Arg] to NPK fertilization in order, to improve fertilizer recommendation during the immature phase of this crop. It reports the results obtained from an experiment conducted on a podzolic soil as Matao, State of Sao Paulo, Brazil. It was a randomized block design in a fractionated factorial experiment 1/2(4x4x4) using 0, 40, 80 and 120 kg.ha-1 of N, P2O5 e K2O. Fertilizers were applied every year starting eight months after planting. During the experimental period evaluations of trunk girth 1.20m above the budgrafting union was measured at each four months. The percentage of plants able for tapping and the period of immaturity were calculated from girth measurements. Soil and plant analysis were performed at several ages. Plant responses to potassium fertilizations were observed starting at 24 months of plant age. Linear NK interaction was frequently observed after 48 months of plant age. Considering the percentage of plants able for tapping, responses were linearly and statistically significant for K fertilization, while N responses were observed in some ocasions. The immaturity period of the crop was significantly affected only by K fertilizers. Besides of this observation, the analysis of the response surface showed that the immaturity period was very dependent on equilibrated relations among nutrients. Unbalanced relations of NPK can delay up to 15 months the beginging of tapping, considering differences between the best and worst treatments. In the absebce of K fertilization there was an antagonistic effect of N and P. Potassium fertilization was essential to reduce the immaturity period.