The urea-fonnaldehyde (UF) polycondensation products are used for particleboard manufacturing; they must have good mechanical resistance and storage properties and low formaldehyde emissions. These qualities are lately achieved by mixing -in various proportions - a classical polycondensation product with oligomers having low polycondensation degree and different urea: formaldehyde ratio. The crystallinity of the products can be directly linked with the size and the structure and reflects the properties of the end product. This paper presents the results of the powder diffraction analysis done on different ureaformaldehyde formulations, obtained after the polycondensation process, before heating in the curing process. Four oligomers, with the urea: formaldehyde ratio of 1:0.... 1:2, are synthesised in the same reaction conditions and the influence of the urea: formaldehyde ratio on the crystallinity degree of the oligomers is discussed. The spectra are compared with those of urea and it can be observed that high formaldehyde content leads to broader peaks, as a result of a more extended polycondensation. This is coupled with a better thermal resistance at 40 degreesC for the oligomers. The crystallinity degree of a polycondensation product with high policondensation degree is also evaluated by XRD.