Surface deformation is as a crucial precursor indicator in the evaluation of highway slope instability. Therefore, the systematic monitoring of deformations is of paramount significance for a comprehensive assessment of highway slope stability. In this work, we employed Interferometric Synthetic Aperture Radar (InSAR) technology to monitor deformations in small-scale highway slopes, specifically focusing on the left slope of the K2+500 section within the Guangkun Expressway Fengkai connection line in Guangdong Province. Deformation monitoring results were derived from C-band Sentinel-1A and L-band ALOS-2 PALSAR2 images. The analysis revealed that acquiring effective deformation phases on the slope using medium-resolution Sentinel-1A images is challenging, primarily owing to the limited geometry size of the slope and the coherence maintenance capability of the C-band. In contrast, the deformation characteristics during the period from October 28, 2017 to April 27, 2019 were effectively revealed through the TCP-InSAR processing of five high-resolution L-band ALOS-2 PALSAR2 images. The InSAR results indicated a prominent deformation zone in the northeastern corner of the slope, exhibiting a maximum deformation velocity of approximately -60 mm/yr. The ongoing deformation process has also affected the secondary berm of the slope, emphasizing the need for the highway management department to focus on preventing and controlling this hidden danger point. Additionally, an obvious deformation area was detected in the southwest trailing edge of the slope. Time series analysis showed that the deformation area accelerated only from October 28, 2017 to April 28, 2018, and then tended to stabilize. Owing to the low temporal resolution of ALOS-2 PALSAR2 images, the underlying mechanism driving this acceleration remains undisclosed. Nevertheless, vigilance towards this potential hazard point by highway management authorities is warranted. In this work, ALOS-2 PALSAR2 data with low temporal resolution were utilized to monitor the deformation characteristics of the slope, yielding some notable results. Building upon this foundation, we discuss the potential applications of L-band LT-1 and NISAR data, anticipating a significant enhancement in the capability of InSAR technology to monitor the fine deformation of small-scale highway slopes.