Different types of un-vulcanized natural rubber, air dried sheets (ADS) and SVR-3L block rubber, were investigated by a new testing method and the results are compared with other mechanical properties. It was found that green strength is strongly reduced if the sample is ther¬mal¬ly treated before testing. Presumably, the decrease of strength is caused by a decrease of branch points, mainly composed of phospholipids, which are linked to the alpha - terminal groups of the rubber molecules. The existence of two different types of branch points is indicated by relaxation spectra, obtained from temperature scanning stress relaxation (TSSR) measurements. The existence of long chain branching is assumed to be important for the high green strength of natural rubber. It is shown, that the green strength strongly decreases, if the sample has passed a mild thermal treatment before testing. This effect has been attributed to a decrease of branch points. The latter are presumably composed of phospholipids, linked at the alpha - terminal groups of the rub¬ber molecules. Proteins, linked at the omega - terminal are also considered to generate branch points via hydrogen bonding, but do not contribute to enhanced green strength. The relaxation spectra, obtained by means of TSSR measurements, exhibit two clearly distinguishable peaks, which are indicating the existence of two different types of branch points. It is assumed, that the first peak at 40 °C is caused by the interaction between omega - terminal groups and proteins, whereas the second peak at 63 °C results from thermal decomposition of branch points, generated by interactions between phospholipids and alpha - terminal groups of the rubber molecules. TSSR measurements turn out as a suitable tool to obtain better understanding of structure - property - relationships of natural rubber.