Phospholipase $C-{gamma}1;(PLC-{gamma}1)$ is an important signaling molecule for cell proliferation and differentiation. $PLC-{gamma}1$ contains two pleckstrin homology (PH) domains, which are responsible for protein-protein interaction and protein-lipid interaction. $PLC-{gamma}1$ also has two Src homology (SH)2 domains and a SH3 domain, which are responsible for protein- protein interaction. To identity proteins that specifically binds to PH domain of $PLC-{gamma}1$, we prepared and incubated the glutathione S-transferase(GST)-fused PH domains of $PLC-{gamma}1$ with COS7 cell lysate. We found that 90 kDa protein specifically binds to PH domain of $PLC-{gamma}1$. By matrix-assisted laser desorption ionization time of flight-mass spectrometry, the 90 kDa protein revealed to be heat shock protein (Hsp) $90{eta}$. Hsp $90{eta}$ is a molecular chaperone that stabilizes and facilitates the folding of proteins that are involved in cell signaling, including receptors for steroids hormones and a variety of protein kinases. To know whether Hsp $90{eta}$ affects on $PLC-{gamma}1$ activity, we performed $PIP_2$ hydrolyzing activity of $PLC-{gamma}1$ in the presence of purified Hsp $90{eta}$ in vitro. Our results show that the Hsp $90{eta}$ dose-dependently inhibits the enzymatic activity of $PLC-{gamma}1$ and further suggest that Hsp $90{eta}$ regulates cell growth and differentiation via regulation of $PLC-{gamma}1$ activity.