Influence of splicing the highly birefringent photonic crystal fiber (HB-PCF) with single mode fiber (SMF) under two different experimental conditions is studied in details. The result shows the birefringence of the HB-PCF can be either increased or decreased significantly, depending on the connection conditions of the HB-PCF end, which are classified as case I (the end is closely butted by another fiber) and case II (the end is in open air). From the experiment and theoretical analysis, it has shown that in case I the retardation change of the spliced section of HB-PCF with 0.2mm in length can be 3.2 times larger than the original value. However, in case II the retardation may be reduced to 72.12% of the original one. The obtained result is important for the design and fabrication of optical fiber devices and sensors based on HB-PCFs.© (2010) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.