A field trial was performed in 2015 and 2016 rice seasons at the farm of Rice Research and Training Center, Sakha, Kafr El-Sheikh, Egypt to study the role of organic fertilizer i.e. compost rice straw 5 t ha^-1 (CRS) and  rice straw 5 t ha^-1 (RS) plus control and potassium treatments namely 60 kg K₂O ha^-1 applied basally before planting (K1), 30 kg K₂O ha^-1 basally plus 2% potassium sulfate (K₂SO₄) as foliar spray at panicle initiation (K2), 2% K₂SO₄  as foliar spray at both panicle initiation (PI) and late booting (LB) periods (K3) plus control (K0) on the yield and its attributes as well as some of grain quality characters of Giza 179 rice variety. The experiment was laid out in a split-plot design with four replications. The organic fertilizer was allocated in the main plots while the sub-plots received potassium treatments. The studied characters were plant height, number of tillers, number of panicle hill^-1, panicle weight, panicle length, number of branches panicle^-1, number of filled grains panicle^-1 and number of unfilled grains panicle^-1, 1000-grain weight, grain and straw yield and some grains quality characters i.e. hulling, milling and head rice percentage as well as available and uptake of potassium .The main results revealed that application of both compost rice straw (CRS) and rice straw (RS) gave the same greatest values of all the previous characters except panicle length which gave insignificant effect. Application of potassium fertilizer at the rate of 60 kg K₂O ha^-1basally applied before planting (K1) or as foliar spray at the rate of 2% K₂O at both panicle initiation (PI) and late booting (LB) produced the highest values of all the studied characters. As for the interaction between organic fertilizer and potassium treatments, results clarified that the combination of 5 t CRS ha^-1with each of60 kg K₂O ha^-1 (K1) or 2% K₂O as foliar spray at both PI and LB (K3) gave the same greatest values in number of panicles hill^-1, filled grains panicle^-1 and grain yield, while panicle weight and straw yieldreached to the maximum values when 5 t RS ha^-1 was combined with K1 and K3. Hulling% reached the maximum value when treated with 5 t CRS ha^-1 while both milling and head rice responded to 5 t RS ha^-1. Treatment of potassium applied as a foliar spray at both PI and LB (K3) produced the highest hulling and milling% while head rice% responded to K2 and K3. The combination of 5 t RS ha^-1 with K1 or K3 gave the highest hulling and milling% while head rice reached the maximum value when each of CRS and RS was combined with each of K1, K2 and K3. Available K reached the maximum value at 30 days after transplanting. Availability of K was the highest under rice straw treatment followed by CRS. The uptake of K reached to the greatest value when either CRS or RS was combined with K1 treatment. It can be concluded that combination of 5 t CRS ha^-1 with K3 (2% K₂SO₄ as a foliar spray at both PI and LB) produced the greatest grain yield and saved about 40 kg K₂O ha^-1. Also, the combination of either 5 t CRS or 5 t RS ha^-1 with K3 treatment improved the grain quality under study.