Tp(R)Ti(OCH3)(3-n)Cl-n (where Tp = hydrotris(pyrazolyl)borate, R = H, Tp* = hydrotris(3,5-dimethylpyrazolyl)borate, R = 3,5-CH3; n = 1, 2, 3) complexes have been tested for ethylene polymerization. Tp(H)Ti(OCH3)(3-n)Cl-n (n = 1, 2) activated with MAO or MMAO showed higher catalytic activity than dimethyl substituted analogues Tp*Ti(OCH3)(3-n)Cl-n (n = 1, 2). Steric effects play a major role on the activity of ethylene polymerization. Successive self-nucleation/annealing (SSA) analysis showed that the polymers produced with use of Tp(H)Ti(OCH3)(3-n)Cl-n (n = 1, 2) have a higher content of chain branching groups than the polymers deriving from Tp(H)TiCl(3). The resulting polymers have melting temperatures characteristic of HDPE.