As an essential macronutrient for plant growth, development, and reproduction, phosphorus (P) is a basic component of cellular structures, functions in energy metabolism and signal transduction cascades, and regulates enzymatic activities. Despite the abundance of P in the soil, the form of P available for uptake by plants, orthophosphate (Pi), is usually present at a low level in the soil due to its precipitation with cations and conversion to organic matter. To circumvent the limited availability of Pi, plants have evolved a repertoire of adaptive responses, so-called P starvation responses, which involve diverse developmental and biochemical processes, to increase Pi acquisition and utilization. To initiate these adaptive responses, P deficiency signaling is transduced via multiple regulatory routes, of which transcriptional or posttranscriptional regulation of gene expression and posttranslational regulation of protein activities have been documented. While several key transcription factors responsible for the transcriptional control of P starvation-responsive (PSR) genes have been identified, microRNAs (miRNAs) have emerged as new players in regulating PSR genes at the posttranscriptional level. miRNAs are endogenous noncoding RNAs 20 to 24 nucleotides in size that are generated from a single-stranded RNA precursor with a hairpin secondary structure. miRNAs negatively regulate gene expression at the posttranscriptional level by base-pairing to their target mRNAs, which often directs mRNA cleavage in plants. Over the past few years, collective studies have revealed significant roles of miRNAs in P deficiency signaling and regulation of Pi homeostasis through the identification and characterization of PSR miRNAs. In this update, we will focus on the roles of PSR miRNAs as effectors and transmitting molecules in P deficiency signaling, the implications of diverse PSR miRNAs in P starvation adaptive responses, and their regulation in response to P deficiency.