The editing efficiencies of prime editing (PE) using ribonucleoprotein (RNP) and RNA delivery are not optimal due to the challenges in solid-phase synthesis of long PE guide RNA (pegRNA) (>125 nt). Here, we develop an efficient, rapid and cost-effective method for generating chemically modified pegRNA (125-145 nt) and engineered pegRNA (epegRNA) (170-190 nt). We use an optimized splint ligation approach and achieve approximately 90% production efficiency for these RNAs, referred to as L-pegRNA and L-epegRNA. L-epegRNA demonstrates enhanced editing efficiencies across various cell lines and human primary cells with improvements of up to more than tenfold when using RNP delivery and several hundredfold with RNA delivery of PE, compared to epegRNA produced by in vitro transcription. L-epegRNA-mediated RNP delivery also outperforms plasmid-encoded PE in most comparisons. Our study provides a solution to obtaining high-quality pegRNA and epegRNA with desired chemical modifications, paving the way for the use of PE in therapeutics and various other fields.