The branching ratio between actinium series and uraniumradium series has been redetermined direetly by means of a counter.The procedure consists in the extraction of protactinium by zirconium phosphate and by titanium oxide from a known uranium mineral,the determination of the efficiency of the counter by means of polonium,and the counting of a-partieles emitted by a known quantity of protactinium preparation. The number of a-particles counted is compared with that caleulated from the uranium contained in the same quantity of mineral. The ratio between them gives the branehing ratio between the two series. The mean value of the ratio obtained with both method of ex-traction is 3,969%,in kood agreement with the value 4% abtained by most predecessors using indirect ionization method. The results obtained by using titanium oxide closely confirms that obtained by using zireonium phosphate,which means that the former is as good an extractant of protactinium as the latter.