PI3Kδ is a key component in the aberrant signaling transduction in B cell malignancy, therefore specific targeting PI3Kδ has become an attractive molecularly targeted therapy for chronic lymphocytic leukemia (CLL). Herein, we describe the discovery and optimization of a series of 5-alkynyl substituted PI3Kδ inhibitors based on the first FDA-approved inhibitor idelalisib. Compound 8d bearing the 1-morpholinohex-5-yn-1-one moiety as the C5-substituent was identified to have high potency against PI3Kδ (3.82 nM) and SU-DHL-6 cells (7.60 nM), respectively. It was 154-fold selective over PI3Kα, 133-fold selective against PI3Kβ, and 24-fold selective against PI3Kγ. Treatment of MOLT-4 and SU-DHL-6 cells with compound 8d for 1 h resulted in reduction of phosphorylation of both Akt (S473) and its downstream S6k1 (T389) in a concentration-dependent manner. Compound 8d showed potent anti-proliferative activity as well against T lymphoblast MOLT-4, suggesting its potential activity in T-cell leukemia.