Orthorhombic HoMn O3 films with well-aligned crystallographic orientations were deposited on LaAl O3 (110) single crystal substrates by using pulsed laser deposition. The nearly perfect b -axis-oriented films provide the opportunity of investigating the orientation-dependent physical property of this material. The temperature dependent magnetization evidently displays an antiferromagnetic ordering near 42 K, irrespective to the direction of applied field. Furthermore, the theoretically expected lock-in transition was clearly observed at around 30 K when field was applied along the c axis and was undetectable along the a and b axes. The 30 K transition was suppressed to 26 K when the applied field increased from 100 to 500 Oe.