Internal Conversion of the 161 keV-and 223 keV-Transitions in 133CsUsing a Ge(Li)--Si(Li)-spectrometer the 161 keV and 223 keV transitions of 133Cs were investigated. The K-conversion coefficients were deduced to be C~g---= 0.205-t-0.007 and c~K=0.0743_+0.0043, respectively. The K/L ratio for the 161 keV transition is 4.72_+ 0.37. From the eg-values, M1 penetration factors of 2-= 8.6__ 3.4 and ~--7 ~+3.o ....... 2.8 were deduced which are inconsistent with known data from angular correlation experiments (2=40_+ 10 and 2=90_+ 13). The penetration factor from K/L-measurement for the 161 keV-transition is 2= 52 _+ 19. A theoretical reinvestigation of the formulas used in the literature appears recommendable. Furthermore, the K/L ratio of the 1770 keV transition of 2~ was determined experimentally to be 5.52 _+ 0.54.